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  • 1992  (46,163)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 1 (1992), S. 1-1 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0932
    Keywords: Muscles paravertébraux ; Muscle multifide ; Anthropométrie ; Lombalgie ; Paraspinal muscles ; Multifidus ; Anthropometry ; Low back pain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary This study of 52 patients (27 men) with recent (18 months) or chronic (〉18 months) low back and unilateral radicular pain symptoms was undertaken to investigate whether wasting of the paraspinal muscle components is generalised or selective. During the patients' routine computed tomographic lumbar spinal scans a standardised transaxial view was obtained along the upper end-plate of the L4 vertebra, and the cross-sectional areas of the paraspinal muscles and their components, multifidus and erector spinae, estimated. Irrespective of whether the symptoms were recent or chronic, multifidus dimensions were significantly greater on the side ipsilateral to the radicular pain symptoms. The results indicate selective changes of multifidus in these patients and possibly reflect an adaptive response by this muscle, such as to an increased role in stabilising the lumbar spine in the face of overall paraspinal muscle atrophy.
    Notes: Résumé Cette étude a été réalisée chez cinquante deux patients (27 hommes, 25 femmes), présentant une lombalgie soit récente (depuis moins de 18 mois), soit chronique (depuis plus de 18 mois) associée à une radiculalgie unilatérale. Le but de la recherche était de déterminer si l'atrophie des muscles paravertébraux était globale ou élective. Lors de l'examen scannographique de routine pratiqué chez ces patients, une coupe transversale a été pratiquée le long du plateau supérieur de la 4e vertèbre lombaire, permettant d'évaluer l'étendue de la surface occupée par ces muscles paravertébraux et leurs composants, plus particulièrement le muscle multifide et le muscle érecteur du rachis. Les résultats indiquent des modifications électives du muscle multifide chez les patients porteurs de lombalgies, et réflètent vraisemblablement une réponse adaptative de ce muscle qui semble jouer un rôle accru dans la stabilisation du rachis lombaire face à l'atrophie globale des muscles paravertébraux.
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  • 3
    ISSN: 1432-0932
    Keywords: Rachis cervical ; Tumeur ; Halo-traction ; Cervical spine ; Tumour ; Halo traction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary A 2-year-old girl suffering from eosinophilic granuloma of the body of C5 presented with subluxation of C5 on C6 and neurological impairment due to cervical cord compression. Following a diagnostic percutaneous biopsy, the child was managed conservatively with halo fraction for 9 weeks and recovered successfully.
    Notes: Résumé Une petite fille de deux ans atteinte d'un granulome éosinophile du corps de C5 présentait une subluxation de C5 sur C6 avec une atteinte neurologique par compression médullaire. Après une biopsie percutanée à visée diagnostique, l'enfant a pu bénéficier avec succès d'un traitement conservateur. La mise en place d'un halo a permis d'appliquer une traction cervicale pendant neuf semaines et d'obtenir ainsi la récupération neurologique.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 1 (1992), S. 43-48 
    ISSN: 1432-0932
    Keywords: Métastases rachidiennes ; Survies ; Tumeurs rachidiennes ; Spinal metastases ; Survival ; Spinal tumours
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Survival analysis of 70 patients with metastatic extradural tumours of the spine is presented. The indication for surgery was rapidly progressive cord compression as a initial manifestation of a malignant disease in 28 cases (40%), a preoperatively known malignant tumour in 28 patients (40%), relapse of cord compression after previous successful radiotherapy in 10 cases (14%), instability in 3 patients (4%) and uncontrolled pain in 1 patient. In 53 procedures (76%) the level of compression was in the thoracic spine, in 9 procedures in the cervical spine (13%) and in 8 procedures in the lumbar spine (11%). All patients had developed a neural deficit before surgery. Fourteen patients (20%) were able to walk prior to surgery, 47 (67%) were paraparetic, and 9 (13%) were paraplegic. Eleven patients died in the first 2 weeks following surgery and out of 59 patients who survived, 39 patients (66%) were able to walk, 11 were paraparetic (19%), and 9 were still paraplegic (15%). Bowel and bladder dysfunction was present in 37 cases (53%) before surgery and in 16 cases (27%) after surgery. Normal sphincter control was regained after 43 (73%) procedures. Persistent back pain was present in 60 patients (86%) before surgery and in 13 patients (22%) after surgery. The mean survival time for all 70 patients was 45.6 weeks. There were 11 early deaths (16%), another 51 patients died from disseminated disease (88%), and 8 patients are still alive (11%) with a mean survival of 133 weeks. A statistically significantly shorter survival was found in patients with lung metastases when compared with the survival of patients with breast metastases and the overall survival of patients with other metastatic tumours.
    Notes: Résumé Ce travail présente une étude de survies chez 70 patients atteints métastases extradurales du rachis. L'indication chirurgicale a été posée dans vingt huit cas (40%) devant une compression médullaire rapidement progressive, première manifestation d'une affection maligne, dans vingt huit autres cas (40%) chez des patients connus avant l'opération pour être porteurs d'une tumeur maligne, dans dix cas (14%) devant une récidive de compression médullaire après une radiothérapie préalablement efficace, dans trois cas (4%) devant une instabilité rachidienne, et dans un cas devant des algies échappant à toute thérapeutique. Dans cinquante trois cas (76%) la compression se situait au niveau du rachis thoracique, dans neuf cas (13%) elle était au niveau du rachis cervical, et dans 8 cas (11%) au niveau du rachis lombaire. Tous les patients avaient présenté un déficit neurologique avant l'opération. Quatorze patients (20%) étaient capables du marcher avant l'opération, quarante sept (67%) étaient paraparétiques et neuf (13%) étaient paraplégiques. Après l'opération, trente neuf patients (66%) furent capables de marcher, onze (19%) étaient paraparétiques et neuf d'entre eux (15%) étaient encore paraplégiques. Un disfonctionnement intestinal et vésical était présent dans trente sept cas (53%) avant l'opération et dans soixante cas (27%) après l'opération. Quarante trois interventions (73%) ont été suivies d'un retour des fonctions sphinctériennes à la normale. Les rachialgies persistantes étaient présentes chez soixante patients (86%) avant la chirurgie et chez treize patients (22%) après l'opération. La durée moyenne de survie pour les 70 patients a été de 45,6 semaines. On a relevé onze décès précoces (16%), 62 patients (88%) sont décédés du fait de la généralisation de leur maladie, et huit patients (11%) sont encore en vie avec une survie moyenne de 133 semaines. Une survie plus courte a été retrouvée de manière significative chez les patients porteurs d'une métastase d'un cancer du poumon, par rapport à ceux atteints de métastases d'un cancer du sein ou d'une autre localisation primitive.
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  • 5
    ISSN: 1432-0932
    Keywords: Disque intervertébral ; Réintervention ; IRM ; Tomodensitométrie ; Saccoradiculographie ; Intervertebral disk ; Reoperation ; Magnetic resonance imaging ; Computed tomography ; Myelography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The differentiation between scar tissue and disk herniation is essential in postdiskectomy problems of the lumbar spine, since reoperation on scar tissue alone is often unfavourable. Epidural scar is a vascularized tissue, and enhancement can be seen after intravenous contrast injection, allowing differentiation from avascular disk material. Ten patients who had previously undergone surgery for lumbar disk herniation and with recurrent symptoms severe enought to warrant repeat surgery were examined by myelography, magnetic resonance imaging (MRI), and computed tomography (CT) before reoperation. MRI was performed with T1- and T2-weighted sequences in sagittal and axial projections before and after intravenous contrast injection. CT scans were obtained before and during intravenous contrast infusion. Reoperation revealed scar tissue, alone or together with disk, in 9 of 10 patients. Enhancement of scar but not of disk material was observed on MRI in 8 cases, but in none on CT. No enhancement of disk was seen with either modality. The correct diagnosis was given by MRI in 9 of 10 patients and by CT in 3 of 10. CT was superior to MRI in only 1 patient, who had a bony stenosis. Myelography could not separate disk from scar in any case. In conclusion, contrast-enhanced MRI was superior to MRI without contrast, CT before and after contrast, as well as myelography in discriminating disk from scar tissue.
    Notes: Résumé Il est essentiel de faire la part entre la fibrose cicatricielle et une hernie discale au cours des récidives symptomatiques survenant après une discectomie lombaire, car la réintervention pour une fibrose cicatricielle isolée aboutit le plus souvent à un résultat défavorable. La fibrose épidurale est un tissu vascularisé qui peut être rehaussé par l'injection intra-veineuse d'un produit de contrast permettant de la distinguer du matériel discal avasculaire. Dix patients ayent été préalablement opérés pour hernie discale et présentant une récidive symptomatique assez sévère pour justifier un éventuel geste chirurgical, ont été explorés avant la réintervention par saccoradiculographie, IRM et tomodensitométrie. L'IRM a été rélisée avec des séquences pondérées en T1 (T1-w) et T2 (T2-w), dans les plans sagittal et transversal, avant et après injection d'un produit de contraste. Les coupes tomodensitométriques ont été réalisées avant et pendant la perfusion intraveineuse du produit de contraste. Chez 9 patients sur 10, la réintervention a mis en évidence le tissue cicatriciel, seul ou accompagné de substance discale. Dans 8 cas l'IRM a permis de mettre en évidence un rehaussement au niveau de la fibrose cicatricielle, sans aucune prise de contraste au niveau du disque; en aucun cas celà n'a été observé au scanner. Quelle que soit la modalité d'exploration, aucun rehaussement n'a été observé au niveau de la substance discale. Le diagnostic correct a été donné par l'IRM dans 9 cas sur 10 et par le scanner dans 3 cas seulement sur 10. La tomodensitométrie ne s'est montrée supérieure à l'IRM que chez un seul patient qui présentait une sténose canalaire osseuse. En aucun cas la saccoradiculographie n'a pu distinguer le disque du tissu cicatriciel. En conclusion, l'IRM avec injection de contraste est effectivement supérieure à l'IRM sans contraste, à la tomodensitométrie avec ou sans injection, ainsi qu'à la saccoradiculographie, pour distinguer la substance discale de la fibrose cicatricielle post-opératoire.
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  • 6
    ISSN: 1432-0932
    Keywords: Sciatique ; Chimionucléolyse ; Chymopapaine ; Lombalgie ; Sciatica ; Chemonucleolysis ; Chymopapain ; Back pain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary In the 11-year period from 1978 and 1988, myelography was performed on 624 patients with suspected herniated lumbar discs. Positive findings, defined as an indentation of the contrast-filled dural sac and/or lack of contrast filling of the nerve roots, were found in 508 (81.4%) patients. Patients with suspected spinal stenosis were excluded from the study. The choice of treatment was determined by the preference of the consultant in charge. In all, 146 patients were treated by chemonucleolysis, 152 patients underwent surgical excision of the disc via laminectomy/fenestration, while 210 patients were listed for further treatment (albeit chemonucleolysis or laminectomy) but sustained relief of symptoms whilst waiting for admission or refused further intervention and consequently continued conservative treatments (such as physiotherapy, manipulations under anaesthetic, epidural or local injections). Following a repetitive questionnaire and clinical review, 78% of those patients that had undergone chemonucleolysis were satisfied with their treatment (i.e. symptoms were either ‘gone’, ‘much better’ or ‘better’). Significantly fewer patients were satisfied after surgical disc excision or conservative treatments (71% and 61%, respectively; P〈0.001). Whereas patients with a short duration of symptoms (less than 1 year) achieved the best outcome after chemonucleolysis and laminectomy, patients with a prolonged history (greater than 2 years) benefitted most from conservative methods. Of those patients in whom symptoms were considered to be worse or the same following treatment, 46%, 51% and 42% were still working following chemonucleolysis, surgery and conservative treatment, respectively. The outcome did not depend upon the size of the disc involved. Although this is a retrospective study, it is the first report to compare the outcome following chemonucleolysis, surgery and conservative methods in patients with disc prolapse confirmed by myelography.
    Notes: Résumé Au cours des onze années allant de 1978 à 1988, 624 patients présentant une suspicion de hernie discale ont été explorés par saccoradiculographie. Des signes positifs comme une encoche d'imprégnation et/ou un défaut de remplissage des gaines radiculaires ont été retrouvés chez 508 patients (81.4%). Les patients présentant une suspicion de sténose lombaire ont été exclus de l'étude. Le traitement a été choisi selon les préférences du praticien responsable. 146 patients ont été traités par chimionucléolyse, 152 ont subi un traitement chirurgical avec laminectomie/fenestration et discectomie. 210 patients en attente d'un traitement complémentaire (bien qu'initialement traités par chimionucléolyse ou laminectomie), ont éprouvé une amélioration de leur symptomatologie alors qu'ils attendaient une réhospitalisation ou ont refusé l'opération et de ce fait ont continué les traitements conservateurs (comme la physiothérapie, les manipulations sous anesthésie et les injections épidurales ou locales). Selon les données du questionnaire et des examens cliniques répétés, 78% des patients traités par chimionucléolyse étaint satisfaits de leur traitement (soit que les symptômes aient disparu, soit qu'ils aient été nettement améliorés ou améliorés). Le nombre de patients satisfaits après discectomie chirurgicale, ou traitement conservateur était significativement moins élevé (respectivement 71% et 61%; P〈0.001). Les patients souffrant depuis moins d'un an ont présenté de meilleurs résultats après nucléolyse et laminectomie, alors que ceux qui présentaient une évolution plus longue (plus de deux ans) ont tiré plus d'avantages des méthodes conservatives. Chez les patients présentant une aggravation ou une persistance des symptômes après le traitement, 46% avaient repris le travail, 51% après chirurgie et 42% après un traitement conservateur. Le résultat était indépendant de la taille de la hernie. Bien que ce travail soit une étude rétrospective, c'est le premier rapport comparant les résultats à la suite de la chimionucléolyse, de la chirurgie et des traitements conservateurs chez des patients présentant une hernie discale confirmée par saccoradiculographie.
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  • 7
    ISSN: 1432-0932
    Keywords: Dysraphie rachidienne occulte de l'adulte ; Dysraphie rachidienne occulte de l'enfant ; Conduite thérapeutique ; Malformation rachidienne ; Occult spinal dysraphism ; Adult pediatric management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Occult spinal dysraphism can present in many ways. In this review the clinical features, pathology, and management of 49 adult and pediatric cases are discussed. Most recent papers agrec that surgery should be performed for clinical deterioration, and many now advise prophylactic surgery for stable or asymptomatic patients. This paper questions the role of prophylactic surgery in such patients. The natural history of occult dysraphism is not known, particularly in the case of adult or asymptomatic patients A conservative management policy, with operation reserced for subsequent clinical or electrophysiological deterioration, is still acceptable in stable or asymptomatic patients. The prospective study of cohorts of patients, with the various forms of occult spinal dysraphism, from units with differing management policies, will help to clarify the natural history of this condition and whether this may be influenced by prophylactic surgery.
    Notes: Résumé Les dysraphies occultes du rachis peuvent revêtir divers d'aspects. Dans cet article sont discutés les faits cliniques, la pathologie et la conduite thérapeutique de 49 cas adultes et pédiatriques. La plupart des articles récents s'accordent sur l'opportunité de la chirurgie lorsque l'état clinique se dégrade, cependant de nombreux auteurs proposent maintenant une chirurgie prophylactique chez des patients stables ou asymptomatiques. Cet article s'interroge sur le rôle de la chirurgie prophylactique chez de tels patients. L'histoire naturelle des dysraphies occultes n'est pas connue et cela est particulièrement vrai chez les patients adultes ou asymptomatiques. Une politique thérapeutique conservatrice, réservant l'intervention aux formes compliquées de détériorations cliniques ou électrophysiologiques, reste toujours valable chez les patients stables et asymptomatiques. L'etude prospective de cohortes de patients, pris dans des unités aux politiques thérapeutiques différentes et porteurs de diverses formes de dysraphie rachidienne occulte, aidera à éclaircir l'histoire naturelle de cette affection et à établir si son évolution peut être influencée par une chirurgie prophylactique.
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  • 8
    ISSN: 1432-0932
    Keywords: Rachis dégénératif ; Fusion lombaire ; Ostéosynthèse ; Vissage translamaire des facettes ; Degenerative spine ; Lumbar fusion ; Internal fixation ; Translaminar facet screw
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary From 1984 to 1988, 70 consecutive lumbar and lumbosacral spine fusions enhanced with translaminar facet joint screws were performed for segmental degenerative disease. Twenty patients had partial decompression of central stenosis, 15 concomitant discectomy, and 19 lateral nerve root decompression. The mean time to fusion was 4.5 months (range 2–7 months). At follow-up (average 45 months; range 24–74 months) 98.5% were judged to have solid fusion. Satisfactory results were observed in 84% of cases, 91% without previous surgery and 75% after previous discectomy. Supplementation of posterolateral fusion by translaminar facet screws significantly improved time to fusion, fusion rate, and clinical outcomes with no significant increased complications.
    Notes: Résumé De 1984 à 1988, 70 arthrodèses lombaires et lombo-sacrées renforcées par un vissage translamaire des articulations interapophysaires ont été réalisées consécutivement pour des atteintes dégénératives segmentaires du rachis. Vingt patients ont eu dans le m^eme temps une décompression partielle pour sténose centrale, 15 une discectomie et 19 une décompression radiculaire latérale. Le délai moyen de fusion a été de 4,5 mois (valeurs extrêmes: 2–7 mois). A distance (délai moyen: 45 mois; valeurs extrêmes: 24–74 mois), 98,5% des patients présentaient une fusion stable. Les résultants satisfaisants ont été globalement observés dans 84% des cas, dans 91% des cas sans chirurgie préalable et dans 75% des cas après discectomie préalable. Le renforcement de la greffe postéro-latérale par le vissage translamaire des facettes améliore de manière significative de délai et le taux de fusion ainsi que les résultats cliniques, sans augmentation significative du taux des complications.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 1 (1992), S. 141-141 
    ISSN: 1432-0932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 10
    ISSN: 1432-0932
    Keywords: Biomécanique ; Implants ; Contraintes ; Rigidité ; Vis pédiculaires ; Biomechanics ; Implants ; Stress ; Stiffness ; Transpedicular fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary A series of 216 biomechanical tests with 36 calf spines were performed to evaluate the rigidity of three newly developed prototypes of transpedicular fixation systems (Spine Fix, AO/ASIF prototype 1, AO/ASIF prototype 2) as compared to the already established Cotrel-Dubousset (CD) system. The Spine Fix system follows the same principle of spinal fixation as the CD system, while the two prototypes of the AO/ASIF group introduce a new concept of spinal reduction and fixation technique, using a three-dimensional adjustable fastening system of transpedicular screws to a longitudinal rod. This allows for correction and fixation of the instrumented vertebra segments in any position. During the tests the main point of interest was whether the newly gained degrees of freedom are associted with a loss of stiffness in the construct. Furthermore, the study evaluated whether transpedicular systems should be optimized from the technological point of view, or whether the stability and rigidity of these systems is determined mainly by the quality of pedicular anchorage. Load displacement was measured using a calf spine model with a precisely defined three-column lesion. Each implant was loaded up to 15 Nm in flexion, extension, lateral bending, and axial rotation. In all tests, the construct behaved in a highly linear fashion (r 2〉0.94). By continously measuring the forces and moments at the cranial end of the spine specimen high accuracy of the tests was achieved (standard deviation: x-axis, 1.74%; y-axis, 1.36%; z-axis, 1.21%). In general, the stifness was found to be highest in lateral bending, follwed by flexion/extension and axial rotation. Spine Fix was the stiffest implant in flexion/extension, AO/ASIF prototype 1 in lateral bending, and AO/ASIF prototype 2 in rotation. In comparison to the CD system (stiffness of CD=100%), differences in stiffness ranged from 77.3% prototype 1 to 140.8% Spine Fix in flexion, from 78.2% prototype 2b to 134.7% Spine Fix in extension, from 108.1% prototype 2b to 213.5% prototype 1 in lateral bending, and from 80.3% prototype 1 to 110.6% prototype 2 in axial rotation. The Spine Fix and prototype 2 systems showed equal or higher stiffness coefficients compared to the CD system. Prototype 1 is significantly more flexible, except in lateral bending, than the CD. From the technical point of view, the two AO/ASIF prototypes allow the correction and fixation of an instrumented vertebra in any position. Prototype 2, despite the additional joint between transpedicular screws and longitudinal rods, shows stiffness comparable to that of the CD system.
    Notes: Résumé Une série de 216 essais biomécaniques ont été effectués sur 36 rachis de veau, afin d'évaluer la rigidité de trois nouveaux prototypes de systèmes de fixation pédiculaires (Spine Fix, Prototype 1 de l'AO/ASIF, Prototype 2 de l'AO/ASIF), par rapport à celle du systéme CD maintenant bien établi. Le système Spine Fix suit la même philosophie de fixation rachidienne que le système CD, alors que les deux prototypes du groupe AO/ASIF introduisent un nouveau concept dans la technique de réduction et de fixation, utilisant un système de fixation tridimensionnel. Ceci permet la correction et la fixation des segments vertébraux instrumentés dans toutes les positions. Durant les essais, le principal point d'intérêt a été de déterminer si les degrés de liberté nouvellement acquis par les prototypes de l'AO/ASIF étaient associés à une perte de rigidité du montage. De plus, cette étude a été réalisée afin d'établir si ces systèmes de fixation pédiculaires doivent être améliorés du point de vue technologique, ou si leur stabilité et leur rigidité sont principalement déterminées par la qualité de l'ancrage pédiculaire. Le déplacement produit par la mise en charge a été mesuré en utilisant pour modèle un rachis de veau porteur d'une lésion bien définie des trois colonnes. Chaque implant a été soumis à une charge allant jusqu'à 15 Nm en flexion, extension, inclinaison latérale et rotation axiale. Dans tous les essais, le montage s'est comporté sur un mode hautement linéaire (r 2〉0.94). Par la mesure continue des forces et des moments à l'extrémité crâniale des spécimens rachidiens, l'évaluation des essais a pu bénéficier d'une haute précision (l'écart-type est de 1.74% sur l'axe des x, 1.35% sur l'axe des y, 1.21% sur celui des z). En général la rigidité a montré une valeur maximale lors de l'inclinaision latérale, cette valeur est un peu plus faible lors de la flexion/extension et de la rotation axiale. La rigidité maximale du Spine Fix est retrouvée lors de la flexion/extension, celle du Prototype 1 de l'AO/ASIF lors de l'inclinaison latérale, et celle du Prototype 2 lors de la rotation axiale. En comparant ces valeurs à celle du système CD (dont la rigidité serait arbitrairement estimée à 100%), les différences de rigidité lors de la flexion, s'étaient de 77.3% pour le Prototype 1, à 140.8% pour le Spine Fix. Lors de l'extension ces différences de rigidité s'étaient de 78.2% pour le Prototype 2b à 134.7% pour le Spine Fix; elles s'étaient de 108.1% pour le Prototype 2b, à 213.5% pour le Prototype 1 dans l'inclinaison latérale et de 80.3% pour le Prototype 1 à 110.6% pour le Prototype 2 en rotation axiale. Le Spine Fix tout comme le Prototype 2 ont montré des coefficient de rigidité égaux ou supérieurs à ceux du système CD. Le Prototype 1 est significativement plus flexible que le CD, sauf en inclinaison latérale. Du point de vue technique, les deux prototypes AO/ASIF permettent la correction et la fixation d'une vertèbre instrumentée dans n'importe quelle position. Le Prototype 2, malgré un dispositif de jonction supplémentaire entre les vis pédiculaires et les tiges, montre une rigidité comparable à celle du système CD.
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  • 11
    ISSN: 1432-0932
    Keywords: Rachis cervical supérieur ; Ligament alaire ; Ligament transverse ; Anatomie ; Biomécanique ; Upper cervical spine ; Alar ligament ; Transverse ligament ; Anatomy ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The occipito-atlanto-axial joint is the most complex one of the human spine. Traumatic or inflammatory lesions in this region may lead to instability and neurological symptoms of clinical importance. This study reports the results of anatomical and biomechanical examination of 13 human upper cervical spine specimens and focuses on the viscoelastic behavior of the alar and transverse ligaments. Non-destructive tensile testing was performed on a uniaxial testing machine with 25 alar and 11 transverse ligaments at three different load rates of 0.1 mm/s, 1.0 mm/s, and 10.0 mm/s. The ligaments were further tested for relaxation over 300 s. Each ligament exhibited an initial neutral zone in which no tensile force could be measured during cyclic testing. This neutral zone was more significant in the alar ligaments than in the transverse ligaments with respect to the measured in situ length of the ligaments (11.2 vs 18.1 mm on average). Increasing axial deformation led to increased load in all ligaments. Hysteresis, i.e., the energy loss exhibited by viscoelastic material subjected to loading and unloading cycles, increased with higher displacement rates and higher tensile forces. In neutral position the alar ligaments were lax in all specimens. During axial rotation both alars tightened. Ligamentous resistance increased as the end of the range of motion (ROM) was approchaed during rotation. The neutral zone explains the laxity of the ligaments in midposition and allows mobility of the upper cervical spine with minimum expenditure of muscular energy. The ligaments become stiffer under higher loads and therefore contribute to a limitation of the ROM in the occipitio-atlanto-axial joint.
    Notes: Résumé L'articulation occipito-atlanto-axoïdienne est l'une des plus complexes du rachis humain. Les lésions traumatiques ou inflammatoires de cette région peuvent conduire à l'instabilité et à des troubles neurologiques importants. Cette étude rapporte les résultats d'une étude anatomique et biomécanique de 13 spécimens de rachis cervical supérieur et met l'accent sur le comportement visco-élastique des ligaments alaires et transverse. Des essais de mise en tension ont été réalisés sur 25 ligaments alaires et 11 ligaments transverses, en restant en deçà du point de rupture. Ils ont été effectués sur un appareil monoaxial, selon trois niveaux de charge différents: 0.1 mm/s, 1.0 mm/s et 10.0 mm/s. La détente ligamentaire a été en outre étudiée pendant 300s. Chaque ligament a montré une zone neutre initiale (NZ) dans laquelle aucune force de tension ne pouvait être mesurée au cours du cycle d'essai. Cette zone neutre était plus importante pour les ligaments alaires que pour les ligaments transverses, compte tenu de la longueur ligamentaire mesurée in situ (11.2 contre 18.1 mm en moyenne). L'augmentation de la déformation axiale a conduit à une augmentation des contraintes dans tous les ligaments. L'hystérésis, c'est à dire la perte d'énergie présentée par le matériel visco-élastique soumis à des cycles de mise en charge et décharge, augmentait avec l'amplitude du déplacement et l'intensité des forces de tension. En position neutre, les ligaments alaires étaient détendus sur tous les spécimens. Lors de la rotation axiale, les deux ligaments alaires se sont mis en tension. La résistance du ligament à la rotation s'est trouvée accrue en fin d'amplitude. La zone neutre explique la laxité des ligaments en position intermédiaire et permet la mobilité du rachis cervical supérieur avec un minimum de dépense d'énergie. Les ligaments se tendent sous des charges plus élevées et par conséquent contribuent à la limitation de ROM dans l'articulation occipito-atlanto-axoïdienne.
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  • 12
    ISSN: 1432-0932
    Keywords: Fracture des pédicules de C2 ; Tétraplégie ; C2 pedicular isthmes ; Tetraplegia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Traumatic spondylolisthesis of the axis is rarely associated with neurological deficit. The authors describe a case of complete tetraplegia due to spinal cord rupture at T1 without any other osteoligamentous lesion at the level. The mechanism of this lesion is discussed; it seems to be due to hyperflexion, with preceding hyperextension responsible for the C2 pedicular fracture.
    Notes: Résumé Le spondylolisthésis traumatique de l'axis est rarement accompagné de déficit neurologique. Les auteurs décrivent un cas de tétraplégie complète due à une rupture de la moelle epinière en T1 sans aucune autre lésion ostéoligamentaire à ce niveau. Le mécanisme de cette lésion est discuté et semble être une hyperflexion précédant l'hyperextension responsable de la fracture des pédicules de C2.
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  • 13
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    Constructive approximation 8 (1992), S. 1-21 
    ISSN: 1432-0940
    Keywords: 41A21 ; 41A30 ; Hermite-Padé approximation ; Padé approximation ; Existence theorems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The problem of approximating a real-valued, locally analytic functions,f(x), by an algebraic function,Q(x), is considered. Existence and uniqueness theorems are obtained under fairly general conditions, including those of “nonnormality.”
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  • 14
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    Constructive approximation 8 (1992), S. 23-33 
    ISSN: 1432-0940
    Keywords: 41A35 ; 41A63 ; Bilinear approximation ; Integral operators ; Sobolev classes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We obtain estimates of approximation numbers of integral operators, with the kernels belonging to Sobolev classes or classes of functions with bounded mixed derivatives. Along with the estimates of approximation numbers, we also obtain estimates of best bilinear approximation of such kernels.
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  • 15
    ISSN: 1432-0940
    Keywords: 41A30 ; 41A35 ; 41A45 ; 41A63 ; Controlled approximation ; Quasi-interpolation ; Strang-Fix theory ; Multivariate approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We establish a result related to a theorem of de Boor and Jia [1]. Their theorem, in turn, corrected and extended a result of Fix and Strang [5] concerning controlled approximation. In our result, the approximating functions are not required to have compact support, but satisfy instead conditions on their behavior at ∞. Our theorem includes some recent results of Jackson [6] and is closely related to the work of Buhmann [2].
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  • 16
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    Constructive approximation 8 (1992), S. 187-201 
    ISSN: 1432-0940
    Keywords: 41A25 ; 41A20 ; Degree of approximation ; Monotone approximation ; Polynomials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We prove that forf∈L p , 0〈p〈1, andk a positive integer, there exists an algebraic polynomialP n of degree ≤n such that $$\left\| {f - P_n } \right\|_p \leqslant C\omega _k^\varphi \left( {f,\frac{1}{n}} \right)_p $$ whereω k ϕ (f,t)p is the Ditzian-Totik modulus of smoothness off inL p , andC is a constant depending only onk andp. Moreover, iff is nondecreasing andk≤2, then the polynomialP n can also be taken to be nondecreasing.
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  • 17
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    Constructive approximation 8 (1992), S. 211-222 
    ISSN: 1432-0940
    Keywords: Primary 46E35 ; Secondary 58F11 ; Fractal dimension ; Wavelets ; Besov space ; Smoothness space
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We study the relation between geometric dimension and smoothness, and give a precise characterization of the fractal dimension of the graph of a function in terms of smoothness classes of functions. We also express the fractal dimension in terms of different classical oscillation measures and in terms of wavelet expansions.
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  • 18
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    Constructive approximation 8 (1992), S. 223-231 
    ISSN: 1432-0940
    Keywords: 46B20 ; 41A65 ; Contractive retract ; Best co-approximation ; Intersection of norm-convex cylinder sets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Two characterizations of ranges of contractive (nonlinear) projections on a finite or infinite dimensionall 1 space are given. One is related to best co-approximation, the other deals with intersections of sets having a simple structure. Concerning the latter the notion of a cylinder set is introduced which serves to replace a certain type of closed half-spaces that are known to be used in characterizing contractive retracts ofl p spaces, 1〈p〈∞,p≠2.
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  • 19
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    Constructive approximation 8 (1992), S. 233-239 
    ISSN: 1432-0940
    Keywords: 30E10 ; 41A10 ; Complex approximation ; Quasiconformal mapping ; Analytic and harmonic functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract LetG⊂C be a finite quasidisk, andf(z) an analytic function inG whose real partu(z)≔Ref(z) is continuous on $$\bar G$$ . Connections between the approximation properties of the functionsu(z) andf(z) are obtained.
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  • 20
    ISSN: 1432-0940
    Keywords: 41A17 ; Markov- ; Bernstein- ; Nikolskii- ; Remez- ; Schur-type inequalities inL p for generalized nonnegative polynomials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We define generalized polynomials as products of polynomials raised to positive real powers. The generalized degree can be defined in a natural way. We prove Markov-, Bernstein-, and Remez-type inequalities inL p (0〈p〈∞) and Nikolskii-type inequalities for such generalized polynomials. Our results extend the corresponding inequalities for ordinary polynomials.
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  • 21
    ISSN: 1432-0940
    Keywords: 41A05 ; 41A63 ; 46E35 ; Function spaces of Besov-Triebel-Lizorkin type ; Whittaker's cardinal series ; Unconditional Schauder bases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let $$I_W f(x) = \sum\limits_{k_1 = - \infty }^\infty \cdots \sum\limits_{k_n = - \infty }^\infty {f\left( {\frac{{2\pi k}}{{2W + 1}}} \right)\prod\limits_{i = 1}^n {\frac{{\sin \left( {\frac{{2W + 1}}{2}x_i - k_i \pi } \right)}}{{\left( {\frac{{2W + 1}}{2}x_i - k_i \pi } \right)}}} }$$ be Whittaker's cardinal series of the functionf. It turns out that the sets of functions with $$\left\| {\left. {\left( {\sum\limits_{W = 1}^\infty {W^{sq} \left| {f(x) - I_W f(x)} \right|^q } } \right)^{{1 \mathord{\left/ {\vphantom {1 q}} \right. \kern-\nulldelimiterspace} q}} } \right|L_p } \right\|〈 \infty$$ or with $$\left( {\sum\limits_{W = 1}^\infty {W^{sq} \left\| {f - I_W f\left| {L_p } \right.} \right\|^q } } \right)^{{1 \mathord{\left/ {\vphantom {1 q}} \right. \kern-\nulldelimiterspace} q}}〈 \infty$$ can be completely described in terms of Besov-Triebel-Lizorkin spaces onR n.
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  • 22
    ISSN: 1432-0940
    Keywords: 41A25 ; 41A30 ; 65D10 ; Multiquadric approximation ; Order of convergence ; Quasi-interpolation ; Radial basis functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The univariate multiquadric function with centerx j ∈R has the form {ϕ j (x)=[(x−x j )2+c 2]1/2, x∈R} wherec is a positive constant. We consider three approximations, namely, ℒ A f, ℒℬ f, and ℒ C f, to a function {f(x),x 0≤x≤x N } from the space that is spanned by the multiquadrics {ϕ j :j=0, 1, ...,N} and by linear polynomials, the centers {x j :j=0, 1,...,N} being given distinct points of the interval [x 0,x N ]. The coefficients of ℒ A f and ℒℬ f depend just on the function values {f(x j ):j=0, 1,...,N}. while ℒ A f, ℒ C f also depends on the extreme derivativesf′(x 0) andf′(x N ). These approximations are defined by quasi-interpolation formulas that are shown to give good accuracy even if the distribution of the centers in [x 0,x N ] is very irregular. Whenf is smooth andc=O(h), whereh is the maximum distance between adjacent centers, we find that the error of each quasi-interpolant isO(h 2|logh|) away from the ends of the rangex 0≤x≤x N. Near the ends of the range, however, the accuracy of ℒ A f and ℒℬ f is onlyO(h), because the polynomial terms of these approximations are zero and a constant, respectively. Thus, some of the known accuracy properties of quasiinterpolation when there is an infinite regular grid of centers {x j =jh:j ∈F} given by Buhmann (1988), are preserved in the case of a finite rangex 0≤x≤x N , and there is no need for the centers {x j :j=0, 1, ...,N} to be equally spaced.
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  • 23
    ISSN: 1432-0940
    Keywords: 41A46 ; 41A15 ; n-Widths ; Exact estimates ; Strong asymptotic estimates ; Classes of periodic functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let $$\tilde W_p^r : = \left\{ {f\left| {f \in C^{r - 1} } \right.} \right.\left[ {0,2\pi } \right],f^{(i)} (0) = f^{(i)} (2\pi ),i = 0, \ldots ,r - 1,f^{(r - 1)}$$ , abs. cont. on [0, 2π] andf (r)∈L p[0, 2π]}, and set $$\tilde B_p^r : = \left\{ {f\left| {f \in \tilde W_p^r ,} \right.\left\| {f^{(r)} } \right\|_p \leqslant 1} \right\}$$ . We find the exact Kolmogrov, Gel'fand, and linearn-widths of $$\tilde B_p^r$$ inL p forn even and allp∈(1, ∞). The strong asymptotic estimates forn-widths of $$\tilde B_p^r$$ inL p are also obtained.
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  • 24
    ISSN: 1432-0940
    Keywords: 41A05 ; 41A63 ; Conditionally negative definite ; Completely monotone ; Radial ; Interpolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Motivated by the problem of multivariate scattered data interpolation, much interest has centered on interpolation by functions of the form $$f(x) = \sum\limits_{j = 1}^N {a_j g(\parallel x - x_j \parallel ),x \in R^s }$$ whereg:R + →R is some prescribed function. For a wide range of functionsg, it is known that the interpolation matricesA=g(∥x i −x j ∥) i,j=1 N are invertible for given distinct data pointsx 1,x 2,...,x N. More recently, progress has been made in quantifying these interpolation methods, in the sense of estimating the (l 2) norms of the inverses of these interpolation matrices as well as their condition numbers. In particular, given a suitable functiong:R + →R, and data inR s having minimal separationq, there exists a functionh s:R + →R +, which depends only ong ands, and a constantC s , which depends only ons, such that the inverse of the associated interpolation matrixA satisfies the estimate ‖A −1‖≤C s h s (q). The present paper seeks “converse” results to the inequality given above. That is, given a suitable functiong, a spatial dimensions, and a parameterq〉0 (which is usually assumed to be small), it is shown that there exists a data set inR s having minimal separationq, a constant $$\tilde C_s$$ depending only ons, and a functionk s (q), such that the inverse of the interpolation matrixA associated with this data set satisfies $$\parallel A^{ - 1} \parallel \geqslant \tilde C_s k_s (q)$$ . In some cases, it is seen thath s(q)=k s (q), so the bounds are optimal up to constants. In certain others,k s (q) is less thanh s (q), but nevertheless exhibits a behavior comparable to that ofh s (q). That is, even in these cases, the bounds are close to being optimal.
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  • 25
    ISSN: 1432-0940
    Keywords: Primary 41A17 ; 42C05 ; Secondary 41A10 ; Freud weights ; Exponential weights ; Orthonormal polynomials ; Christoffel functions ; Markov-Bernstein inequalities ; Potentials ; Discretization of potentials ; Nevai's conjecture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We obtain upper and lower bounds for Christoffel functions for Freud weights by relatively new methods, including a new way to estimate discretization of potentials. We then deduce bounds for orthogonal polynomials onℝ thereby largely resolving a 1976 conjecture of P. Nevai. For example, let W:=e −Q, whereQ:ℝ→ℝ is even and continuous inℝ, Q" is continuous in (0, ∞) andQ '〉0 in (0, ∞), while, for someA, B, $$1〈 A \leqslant \frac{{(d/dx)(xQ'(x))}}{{Q'(x)}} \leqslant B,x \in (0,\infty )$$ Leta n denote thenth Mhaskar-Rahmanov-Saff number forQ, andL〉0. Then, uniformly forn≥1 and |x|≤a n (1+Ln −2/3), $$\lambda _n (W^2 ,x) \sim \frac{{a_n }}{n}W^2 (x)\left( {\max \left\{ {n^{ - 2/3} ,1 - \frac{{|x|}}{{a_n }}} \right\}} \right)^{ - 1/2}$$ Moreover, for all x εℝ, we can replace ∼ by ≥. In particular, these results apply toW(x):=exp(-|x|α), α〉1. We also obtain lower bounds for allx εℝ, when onlyA〉0, but this necessarily requires a more complicated formulation. We deduce that thenth orthonormal plynomialp n (W 2, ·). forW 2 satisfies $$\mathop {\sup }\limits_{x \in \mathbb{R}} |p_n (W^2 ,x)|W(x)\left| {1 - \frac{{|x|}}{{a_n }}} \right|^{1/4} \sim a_n^{ - 1/2}$$ and $$\mathop {\sup }\limits_{x \in \mathbb{R}} |p_n (W^2 ,x)|W(x) \sim a_n^{ - 1/2} n^{1/6} .$$ In particular, this applies toW(x):=exp(-|x|α), α〉1.
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  • 26
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    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper presents a formulation of continuum theory for nematic liquid crystals based upon the balance laws for linear and angular momentum, that derives directly expressions for stress and couple stress in these transversely isotropic liquids. This approach therefore avoids the introduction of generalised forces or torques associated with the director describing the axis of transverse isotropy.
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  • 27
    Electronic Resource
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    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The condition for interface equilibrium, in which the Eshelby's energymomentum tensor is recognized as a generalization of the chemical potential in Gibbs' classical results, is used to evaluate the stability of the shape of inclusions in an infinite body with Eshelby's results for infinitesimal transformation strains.
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  • 28
    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Blotekjaer hydrodynamical model for charge carriers transport in semiconductors is reconsidered from the viewpoint of extended thermodynamics. In particular the Blotekjaer original closure of the moment equations is shown to be equivalent to that obtained by applying the entropy principle.
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  • 29
    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An analysis of discontinuity wave propagation across a constant state for a relativistic charged fluid with finite electric conductivity is performed. Beside thecontact wave usual in fluid dynamics, acharge wave arises which propagates with the drift speed of the ions. The remaining eight waves are all coupled together and reduce to magnetoacustic and Alfven waves when the electric conductivity tends to infinity, while they become purely electromagnetic waves when the electric permutivity and the magnetic permeability of the medium are the same as in vacuo.
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  • 30
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Geological investigations of the crown-of-thorns starfish (COTS) have concluded that outbreaks are not only recent but also have occurred in the past. The evidence lies in the abundance of COTS skeletal elements found both on the sea floor and within the underlying sedimentary record. These studies are flawed in three respects. First, the processes of fossil preservation from the living population to the fossil assemblage have been ignored. Second, it has not been demonstrated that the fossil skeletal elements representing alleged outbreak populations of starfish are of the same age. Third, the existence of a relationship between the number of COTS skeletal elements sampled from the sedimentary record and the relative abundance of COTS in the once living population has not been substantiated. The limitations introduced when studying the fossil record need to be established through taphonomic analyses of the COTS. Techniques which will allow greater temporal resolution of skeletal element age include amino-acid geochronology, analysis of sedimentation mode and rate, and correlation among sub-surface cores. In order to establish a relationship between the number of fossil COTS elements and the original population size, methods must be developed which will relate the number of fossil skeletal elements to the relative abundance of starfish in both the fossil and death assemblages and then to relate the latter to the relative size of the original population. When these approaches are used together it may be possible to make some estimate of relative COTS abundances based on data contained in the fossil record.
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  • 31
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A total of 1655 crown-of-thorns starfish skeletal elements were recovered from 237 surface sediment samples from Davies, Centipede, Myrmidon, Hope, Holbourne Island, 22–110, Gannet Cay and Lady Musgrave Island Reefs of the central and southern sectors of the Great Barrier Reef. Three categories of reef may be recognised on the incidence of Acanthaster planci skeletal elements in surface sediment from these and previously studied reefs: category A (abundant, 〉12 elements kg1-), category C (common, 3–8 elements kg-1) and category C (rare, 0–0.1 elements kg-1). These categories parallel estimates of crown-of-thorns populations in the period 1986–1990. “A” reefs have generally experienced high intensity outbreaks, “C” reefs less intense or perhaps less frequent outbreaks and “R” reefs have had little or no crown-of-thorns presence. The incidence of crown-of-thorns skeletal elements in surface sediment potentially provides an indication of population densities and outbreaks over a time scale of several decades. A perspective of contemporary crown-of-thorns incidence on the many reefs of the GBR lacking direct observational records may thereby be obtained. For Holbourne Island a comparison was made of element incidence in an area of known mass mortality induced by poisoning with a control area that was undisturbed. The incidence of A. planci skeletal elements is comparable in the two areas and similar to the incidence established for other reefs such as Green Island and John Brewer where high intensity outbreaks are known to have occurred. A direct relationship between high incidence of elements in surface sediment and mass mortality following outbreak events is indicated.
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  • 32
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The nature and interpretation of the fossil record of Acanthaster planci from the GBR is reviewed in the light of comments from Keesing et al. (1992) and Pandolfi (1992). Skeletal remains of A. planci in reef-top sediment of many reefs has been derived from very large numbers of individuals, indicating substantial, long-term mortality at reef-top locations. The fossil record provides useful perspective on mortality patterns in the absence of substantive ecological data. The incidence of skeletal elements on reefs where they are abundant cannot be adequately accounted for by the mortality of non-outbreak populations as estimated by recent surveys. Analysis of all available data reaffirms a relationship between the incidence of skeletal elements in surface sediment and observed outbreak history. There is no presently identified taphonomic mechanism by which the accumulation of A. planci skeletal elements released on death might be systematically biased relative to other skeletal components of reefal sediment. Because of skeletal degradation, physical transport and extensive bioturbation that applies in shallow-water reefal sediment, reconstructive taphonomic analysis of A. planci skeletal remains is not achievable. Core sediment, on which interpretation of the longterm fossil record of A. planci is based, is homogeneous, unstratified, and has experienced substantial time averaging due to pervasive bioturbation. Extensive bulk sediment dating has shown that the cores have retained a general age structure but fine-scale stratigraphic detail, required for the recognition of outbreak events from the fossil record available in reefal sediment is unlikely. As required by the principle of simplicity, the proposition that abundant A. planci skeletal elements found in sediment from Green Island, John Brewer and other reefs of the GBR represent the time-averaged product of outbreaking populations should be adopted as the favoured working hypothesis. Other alternative explantions have been advanced but all require patterns or processes that have yet to be substantiated.
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  • 33
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The rate of decomposition of 67 crown-of-thorns starfish was monitored over 7–9 days on 2 reefs of the Great Barrier Reef in 7 permanent quadrats in different depths and habitats. The pattern of decomposition was similar in all quadrats irrespective of the site or depth. Many different organisms, including crown-of-thorns starfish, fed on or scavenged the remains. Despite this activity the remains could be recognised as crown-of-thorns starfish for up to 5 days. The reason for the sudden disappearance of starfish at the ends of outbreaks is briefly discussed.
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  • 34
    ISSN: 1432-0983
    Keywords: Schizosaccharomyces pombe ; Fertility gene ; Thermo-conditional mutant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A recessive mutant allele, mef1-84, of a novel locus mapping on the left arm of chromosome I, between ade3 and ura1, 5 cM apart from lys5, confers temperature-sensitive growth and mating deficiency at the nonrestrictive temperatures for growth. Two other mutations suppress the phenotype conferred by mef1-84: sts1-1 suppresses the temperature-sensitive growth only, and smd1-35 suppresses both temperature-sensitive growth and mating deficiency.
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  • 35
    ISSN: 1432-0983
    Keywords: Trichoderma ; Transformation ; Hygromycin B resistance ; Benomyl resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have developed a transformation system for Trichoderma hamatum and Trichoderma harzianum Rifai, using dominant markers for selection based on the Escherichia coli hygromycin B phosphotransferase gene (hph) and the β-tubulin gene (bml) from Neurospora crassa, respectively. Transformation frequencies and protoplast regeneration were low in both species. All the T. hamatum hygromycin-resistant transformants analysed were mitotically stable, in contrast to those of T. harzianum derived by benomyl resistance, in which only 50% of the transformants analysed were stable. Molecular analysis of transformants showed the integration of the transforming DNA into the genome and indicated that the number and sites of integration varied among the transformants.
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  • 36
    ISSN: 1432-0983
    Keywords: S. cerevisiae ; Lysine biosynthesis ; LYS5 gene ; Subclone ; Enzyme activity ; S1 analysis ; DNA homology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The LYS5 and LYS2 genes of Saccharomyces cerevisiae are required for the synthesis of α-aminoadipate reductase in the lysine pathway. The LYS5 gene, originally cloned as a DNA insert of the plasmid pSC5, has been subcloned on a 3.2 kb SphI-Sau3AI DNA fragment of the recombinant plasmid pSR7. An internal 2.1 kb HpaI-HpaI DNA fragment of the subclone, upon Southern hybridization, exhibits homology with HpaI-restricted wild-type S. cerevisiae genomic DNA. The lys5 + transformants exhibited α-aminoadipate reductase activity similar to that of wild-type cells. S1 nuclease analysis localizes the transcription initiation site relative to the detailed restriction map, and reveals the direction of transcription, as well as the transcript size of the LYS5 gene which can be no greater than 1.65 kb. From this it is estimated that the encoded polypeptide is appreciably smaller than the 4 kb LYS2 gene product. These results provide a physical and biochemical characterization of the cloned LYS5 gene. Based on these observations, it is concluded that the LYS5 gene encodes a relatively small polypeptide of the large heteropolymeric α-aminoadipate reductase.
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  • 37
    ISSN: 1432-0983
    Keywords: DNA fingerprinting of Trichoderma ; Trichoderma reesei ; RFLP ; Strain classification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have analyzed nine different species of the filamentous fungus Trichoderma and three strains of T. reesei for the presence of hypervariable loci in their genomes by hybridization with simple repeat oligonucleotides [(CT)8, (GTG)5, and (GACA)4]. On the basis of the DNA-fingerprints obtained, the Trichoderma aggregate is re-classified into five groups: I (T. reesei, T. todica), II (T. polysporum, T. longibrachiatum, T. koningii, and T. pseudokoningii), III (T. virgatum), IV (T. saturnisporum) and V (T. harzianum). These results contradict the claim that T. reesei is a subspecies of T. longibrachiatum. Furthermore, hybridization with (CA)8 allowed a subdivision of group II, wherein T. pseudokoningii formed a subgroup, IIb, which is highly homologous with, but distinct from subgroup IIa. The results show that RFLP analysis may be used to re-classify the Trichoderma aggregate.
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  • 38
    ISSN: 1432-0983
    Keywords: Trichoderma reesei ; Cellobiohydrolase genes ; Cellulase formation ; Trichoderma sp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Eight different species of Trichoderma (T. virgatum, T. longibrachiatum, T. harzianum, T. pseudokoningii, T. polysporum, T. koningii, T. todica, T. saturnisporum), and three strains of T. reesei [QM 6a (wildtype), QM 9123 and QM 9414 (derived mutants)] were found to contain single copies of the cellobiohydrolase genes cbh1 and cbh2 in their genome. This was demonstrated by hybridization of the respective chromosomal DNAs with the corresponding gene fragments of T. reesei QM 9414. According to the relative position of cbh1 and cbh2 in Southern blots, T. harzianum, T. virgatum and T. saturnisporum were clearly distinguishable as unique species. Despite the presence of both cbh genes, these species did not form detectable cellobiohydrolase (CBH) I or II, or exhibit any cellulase activity. All other taxa were identical with respect to the genomic position of cbh1, formed two groups with respect to the position of cbh2, and produced varying amounts of CBH I and II. In all cases CBH I and II production correlated with the relative amount of cbh1- and cbh2-mRNA found. This was particularly true for the three strains of T. reesei, which secreted different amounts of CBH I and II, their efficiency to transcribe cbh1 and cbh2 having been increased as a result of mutation for higher cellulase production.
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  • 39
    ISSN: 1432-0983
    Keywords: Neurospora ; Tomato ; Nitrate reductase ; Nitrate regulation ; GATA-binding factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nit-2 gene of Neurospora crassa encodes a trans-acting regulatory protein that activates the expression of a number of structural genes which code for nitrogen catabolic enzymes, including nitrate reductase. The NIT2 protein contains a Cys2/Cys2-type zinc-finger DNA-binding domain that recognizes promoter regions of the Neurospora nitrogen-related genes. The NIT2 zincfinger domain/β-Gal fusion protein was shown to recognize and bind in a specific manner to two upstream fragments of the nia gene of Lycopersicon esculentum (tomato) in vitro, whereas two mutant NIT2 proteins failed to bind to the same fragments. The dissociation kinetics of the complexes formed between the NIT2 protein and the Neurospora nit-3 and the tomato nia gene promoters were examined; NIT2 binds more strongly to the nit-3 promoter DNA fragment than it does to fragments derived from the plant nitrate reductase gene itself. The observed specificity of the binding suggests the existence of a NIT2-like homolog which regulates the expression of the nitrate assimilation pathway of higher plants.
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  • 40
    ISSN: 1432-0983
    Keywords: Aspergillus ; Neurospora ; Isocitrate lyase ; Glyoxysome ; Acetate metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nucleotide sequences of the genes encoding the acetate-inducible glyoxylate cycle enzyme isocitrate lyase from the ascomycete fungi Aspergillus nidulans (acuD) and Neurospora crassa (acu-3) are presented. The respective A. nidulans and N. crassa genes are interrupted at identical positions by two introns and encode proteins of 538 and 543 amino acids, which have 75% identity. The predicted protein sequences do not demonstrate the C-terminal tripeptide S-K-L that has been implicated in peroxisomal targeting and found in the glyoxysomally located enzyme malate synthase from the same species. However, the protein sequences do exhibit a partial repeat which, in common with malate synthase, is located in regions that are absent from, or non-homologous with, the E. coli enzyme, which is not compartmentalized.
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  • 41
    ISSN: 1432-0983
    Keywords: Transcription control ; Penicillium chrysogenum ; Penicillin biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The presence of a transcriptional control simultaneously affecting the expression of the three penicillin biosynthetic genes, pcbAB, pcbC, and penDE (pen genes), was demonstrated in Penicillium chrysogenum. Using probes specific to each gene, it was observed that the highest level of expression of the pen genes occurred during exponential growth, in both the original ancestral strain (NRRL1951) and a high-penicillin producing strain P2. Expression also occurred in the presence of high concentrations of glucose, indicating that carbon catabolite repression was not directly involved in the regulation. Transcription of the pen genes appeared to cease as the growth rate decreased. Growth was limited in a fermenter by the rate of oxygen transfer. The phosphoglycerate kinase gene (pgk), used as a control, was strongly induced by the reduced oxygen levels, suggesting a stress-related response. By maintaining optimum growth conditions in fermenters, no induction of the pgk gene was observed whereas expression of the pen genes could be maintained. It was also possible to re-establish expresion of the pen genes, after normal cessation, by the addition of cycloheximide to the culture medium.
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  • 42
    ISSN: 1432-0983
    Keywords: Transformation ; Stability ; Hygromycin B resistance ; Rice blast fungus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Magnaporthe grisea was transformed with cosmid pAN7-2 encoding hygromycin B resistance but containing no homology with the M. grisea genome. Rearrangement of the integrated DNA was detected in several hygromycin B-resistant progeny from cross Guy11-T10-1 (a single-copy integration site transformant)x2539 (sensitive wild-type parent), but not in hygromycin B-resistant progeny from four other crosses. Transformants produced typical lesions when inoculated onto host plants. Southern hybridization revealed rearrangements of integrated DNA in single conidial isolates of highcopy transformant 2539-T1-1 re-isolated from host plants, characterized by excision of one or more copies of the transforming plasmid. Plasmid loss and rearrangement were also observed within single conidial isolates derived from transformant 2539-T1-1 following ten asexual generations on non-selective agar medium. These examples of instability of integrated DNA in M. grisea transformants suggest that caution should be exercised in the use of transformation for assessing the phenotypic effects of specific introduced genes.
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  • 43
    ISSN: 1432-0983
    Keywords: Phycomyces blakesleeanus ; β-carotene ; End-product regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The regulation of carotenogenesis in the fungus Phycomyces blakesleanus is mediated by several gene products and influenced by light, retinol, and other external agents. De-regulation of the biosynthetic pathway is found in the deep-yellow carS mutants and the white carA mutants. The carA, carS recombinants are yellow; their β-carotene content is intermediate between that of strains carrying each of the two mutations. Mutagen exposure of a deep-yellow carS mutant led to the isolation of white double-mutants which become yellow in the presence of retinol. They carry two very closely linked mutations in the carS gene. When separated in different organisms, each of these mutations results in a deep-yellow phenotype. Our results support the idea that two gene products recognize the beta rings of β-carotene and shut off biosynthesis when enough β-carotene has been made. The modified gene product present in the white carS mutants stops synthesis in the absence of β-carotene.
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  • 44
    ISSN: 1432-0983
    Keywords: Aphanocladium album ; Chitinase gene ; Fusarium oxysporum ; Heterologous expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Recombinant clones from a cDNA library of an Aphanocladium album chitinase-overproducing mutant strain were isolated by screening with antiserum against a 39 kDa chitinase purified from this hyperparasitic fungus. Analysis of the isolated positive clones indicated that most of them carried the same cDNA. A cDNA from this group was used as a hybridization probe to isolate an 8 kb DNA fragment from a genomic library of the wild-type strain. The chitinase 1 gene was mapped to this fragment by two independent approaches. Its partial DNA sequence was in perfect agreement with an amino-terminal peptide sequence obtained by sequencing 23 amino acids of the 39 kDa chitinase. Its transfer in Fusarium oxysporum resulted in a transformant producting both a protein of about 39 kDa that cross-reacted with the chitinase antiserum and a chitinase activity that was inhibited by the same antiserum. Northern blot analysis indicates that the cloned chitinase gene was subject to catabolite repression and appeared inducible by chitin.
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  • 45
    ISSN: 1432-0983
    Keywords: Cryptomonads (Pyrenomonas salina) ; Plastid DNA ; SSUrRNA sequence ; Plastid evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cryptomonads are thought to have arisen from a symbiotic association between a eukaryotic flagellated host and a eukaryotic algal symbiont, presumably related to red algae. As organellar DNAs have proven to be useful tools in elucidating phylogenetic relationships, the plastid (pt) DNA of the cryptomonad alga Pyrenomonas salina has been characterized in some detail. A restriction map of the circular 127 kb ptDNA from Pyrenomonas salina was established. An inverted repeat (IR) region of about 5 kb separates two single-copy regions of 15 and 102 kb, respectively. It contains the genes for the small and large subunit of rRNA. Ten protein genes, coding for the large subunit of ribulose-1,5-bisphosphate carboxylase, the 47 kDa, 43 kDa and 32 kDa proteins of photosystem II, the ribosomal proteins L2, S7 and S11, the elongation factor Tu, as well as the α- and β-subunits of ATP synthase, have been localized on the restriction map either by hybridization of heterologous gene probes or by sequence homologies. The gene for the plastidal small subunit (SSUr) RNA has been sequenced and compared to homologous SSU regions from the cyanobacterium Anacystis nidulans and plastids from rhodophytes, chromophytes, euglenoids, chlorophytes, and land plants. A phylogenetic tree constructed with the neighborliness method and indicating a relationship of cryptomonad plastids with those of red algae is presented.
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  • 46
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    Current genetics 21 (1992), S. 91-91 
    ISSN: 1432-0983
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 47
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    Current genetics 21 (1992), S. 83-84 
    ISSN: 1432-0983
    Keywords: Yeast ; Transformation ; Thio compound ; Stationary phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A fast yeast-transformation technique has been developed by adding thio compounds to alkali-ion based protocols and incubating at 45°C. This procedure is especially recommended for cells from stationary phase at a density up to 2.5×108 cells/ml. It involves only one step for the preparation and transformation of competent cells within 30 min. The yield was more than 104 transformants/μg plasmid DNA. This protocol is easy to scale up for many DNA samples and is also applicable for yeast cells from different types of storages.
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  • 48
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    Current genetics 21 (1992), S. 121-124 
    ISSN: 1432-0983
    Keywords: Zygomycetes ; Parasitella simplex ; Transformation ; Parasitism ; Absidia glauca
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The facultatively parasitic zygomycete Parasitella simplex was transformed to neomycin resistance by a vector, which had been developed primarily for transformation of its host Absidia glauca. This plasmid, pAmNEF21, contained the bacterial resistance gene for neomycin (NPTII) under the control of the promoter region from the gene for elongation factor 1 (tef) isolated from A. glauca. Both flanking regions of the marker gene contain parts of the structural tef gene. DNA isolated from two Parasitella transformants was re-transformed in E. coli and the resulting plasmids, pAt21 and pAt35, were analyzed. The restriction map and Southern blot analysis show that both plasmids are rearranged. They had lost the structural tef information and were found to contain new DNA fragments, which were identical in both cases. Southern blot analysis of the transformants indicates that the rearranged plasmids are present in the fungal transformants and that the changes are not the result of re-transformation in E. coli. Plasmids were only recovered after growth under selective conditions. Southern blot analysis and re-transformation with undigested transformant DNA shows that the plasmids are replicated autonomously.
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  • 49
    ISSN: 1432-0983
    Keywords: Mitochondrial genome size ; Repeated sequences ; Ribosomal RNA genes ; Nonflowering plants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report the first estimates of genome size and complexity for mitochondrial DNAs (mtDNAs) from nonflowering land plants. The mtDNA of Onoclea sensibilis (sensitive fern) is approximately 300 kb in size, while that of Equisetum arvense (common horsetail) is at least 200 kb. Sufficient mtDNA of Onoclea was available to permit an estimation of the copy number and a linkage analysis of nine mitochondrial genes. Six of these genes appear to be present in only one or two copies in the Onoclea genome, whereas three other genes are present in multiple copies. Five of the approximately ten genes encoding 26S rRNA are located on a large, 〉10kb, dispersed repeat that also contains closely linked genes for 18S rRNA and the alpha subunit of ATPase (atpA). The other 26S genes belong to a second dispersed repeat family of 〉8 kb whose elements do not contain any other identified genes. Because flowering plant mtDNAs are also large and contain dispersed, gene-containing, repeats, it appears that these features arose early in the evolution of land plants, or perhaps even in their green algal ancestors.
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  • 50
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Mitochondria ; Cytochrome c oxidase subunit 1 ; RNA processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Eighteen nuclear mutants of the yeast Saccharomyces cerevisiae, each disturbed in the biosynthesis of the mitochondrially encoded cytochrome c oxidase subunit 1 (cox 1) and each representing a distinct complementation group, have been examined to identify the level at which COX1 expression is affected. RNA blotting revealed that most have a defect in the processing of COX1 precursor-mRNA; only a few are defective in COX1 transcription and/or pre-mRNA stability. In most RNA-processing mutants, the absence of the COX1 messenger results from a defect in the splicing of one or more COX1 introns. In turn, this defect can be ascribed to a mutation in a nuclear gene which is either directly involved in splicing or else acts indirectly by impairing COX1 translation.
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  • 51
    ISSN: 1432-0983
    Keywords: mtDNA ; Recombination ; CMS ; N. sylvestris
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two cytoplasmic male-sterile plants (CMSI and CMSII) were obtained by protoplast culture in Nicotiana sylvestris. Both plants showed large deletions (up to 50 kb) in their mitochondrial DNA. Restriction maps of the reorganized regions suggested that the deletions occurred via two homologous recombination events (rec. 1 and rec. 2) in the parental mitochondrial genome. With the exception of nad5, no mitochondrial DNA polymorphism could be detected between parental and CMS lines using different heterologous genes probes. A sequence homologous to the Oenothera nad5 mitochondrial gene was located close to the CMSI-specific rec. 2 region. Moreover, a cDNA probe corresponding to total mitochondrial RNA from the parent line was found to hybridize to mitochondrial DNA fragments involved in the rec. 1 event common to both CMS lines, suggesting that rec. 1 lies in a transcribed region. Cytoplasmic male sterility in the Nicotiana sylvestris CMS mutants could be due either to gene deletion or to a regulatory effect of such a deletion on mitochondrial gene expression, rather than to the presence of specific polypeptides as has been shown in the T cytoplasm of maize, or in CMS Petunia.
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  • 52
    ISSN: 1432-0983
    Keywords: Claviceps purpurea ; Linear mitochondrial plasmid ; Transcription initiation ; Western blots ; DNA/RNA polymerase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Expression of the linear mitochondrial (mt) plasmid pClK1 of strain K of the ascomycete Claviceps purpurea was studied at the RNA and protein level. Using strand-specific probes two major transcripts were detected, corresponding to ORF1 and ORF2 of the plasmid, which most likely code for a DNA-polymerase and an RNA-polymerase, respectively. Primer extension experiments showed that both transcripts start at identical positions from opposite sides within the terminal inverted repeat (TIR). The initiation sequence corresponds to the proposed general mt initiation consensus-sequence. Conserved parts of the putative polymerase ORFs were expressed in an E. coli system and used to prepare antisera. In Western experiments the presence of corresponding proteins was demonstrated in a strain carrying plasmid pClK1, whereas a plasmid-free strain lacked these polypeptides. The sizes of these proteins are in good accordance with the sizes derived from the coding capacity of ORF1 and 2.
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  • 53
    ISSN: 1432-0983
    Keywords: Yeast ; Transcription ; Mitochondria ; RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In yeast (S. cerevisiae) the stringent response is known to include rapid, selective, and severe transcriptional curtailment for genes specifying cytoplasmic rRNAs and r-proteins. We have shown that transcription of the mitochondrial 21S rRNA gene is also congruently and selectively curtailed during the yeast stringent response. Using an in vitro transcription assay with intact organelles from both ϱ+ and ϱ− strains, we show here that the mitochondrial stringent response includes not only transcription of the 21S and 16S rRNA genes, but also that of organellar genes specifying non-mitoribosome-related products. Stringent organellar transcriptional curtailment is identical when cells are starved for a required (marker) amino acid or when they are subjected to nutritional downshift, and the relative level of that transcriptional curtailment following either perturbation is the same in cells growing on fermentative (repressing) or purely respiratory carbon sources. These results confirm that the mechanism governing mitochondrial gene expression during a stringent response is specified outside the organelle, and they show that this transcriptional control mechanism is not immediately subject to glucose repression. In all strains examined, stringent organellar gene expression requires a mitochondrial promoter, suggesting that the regulatory mechanism which functions during the stringent response operates primarily at transcriptional initiation.
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  • 54
    ISSN: 1432-0983
    Keywords: Linear plasmids ; Phylogenetic trees
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Relative phylogenetic distances were estimated for those linear plasmids for which sequencing data were available by comparing the amino-acid sequences of the putative DNA- and RNA-polymerases, and phylogenetic trees were calculated. The relationships obtained accord well with those indicated by other structural characteristics of these genetic elements. It is obvious that linear plasmids constitute a separate group of genetic traits when compared with those of the adenoviruses. However, an overall relationship to these viruses is evident. Among the linear plasmids at least two main groups can be recognized, namely the cytoplasmically and the mitochondrially localized elements.
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  • 55
    ISSN: 1432-0983
    Keywords: Saccharomyces ; Invertase ; Cytochromes ; Gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The RPS5 gene has been characterised through its ability to reduce invertase production by the SUC5 gene. In this paper we show that RPS5 acts by maintaining low levels of SUC5 mRNA. We also show that RPS5 acts on the SUC1 and SUC4 genes but not on SUC2 and SUC3, which are members of the SUC family. RPS5 also shows a pleiotropic effect on the amount of mitochondrial cytochromes.
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  • 56
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Aminoacyl-tRNA synthetase mutant ; PGK overexpression ; In vivo misreading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The hts1.1 temperature-sensitive histidinyl-tRNA synthetase mutation enables Saccharomyces cerevisiae to be starved for His-tRNAHis by upshift to the non-permissive temperature of 38°C. If yeast behaves similarly to bacterial and mammalian cells, this lack of His-tRNAHis should greatly enhance misreading at histidine codons (CAU/CAC) by Gln-tRNAGln, resulting in substitution of the neutral amino acid glutamine in place of histidine, a basic amino acid. Such misreading causes the isoelectric point (pI) of proteins to shift to lower values, and is readily detectable as “stuttering” on two-dimensional (2D) protein gels. By gel analysis of pulse-labelled proteins of hts1.1 yeast cells that were overexpressing phosphoglycerate kinase (PGK), our study sought to detect this specific translational error in PGK protein. It was not detected by this relatively sensitive technique, indicating that missense errors due to glutamine insertion at histidine codons do not occur in yeast at the readily-detectable level found in bacterial and mammalian cells.
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  • 57
    ISSN: 1432-0983
    Keywords: Yeast ; DNA-polymerase α ; Cell cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The 5′ ACGCGT3′ MluI motif, which is found in the upstream region of several yeast DNA-synthesis genes which are periodically expressed during the mitotic cell-cycle, is present twice in the 5′ non-coding region of the DNA-polymerase α gene (POL1). Deletion, of the most distal repeat does not affect POL1 transcription, while the adjacent 40 base-pair (bp) downstream sequence is necessary both for the proper level and the fluctuation of POL1 mRNA. This region contains the 5′ACGCGTCGCGT3′ sequence, which is sufficient to control periodic transcription of a CYC1-lacZ reporter gene with the same kinetics observed for POL1. The adjacent 29 bp AT-rich region does not show any activity by itself, but it acts synergistically in conjunction with at least one MluI hexamer to stimulate CYC1-lacZ expression. By further deletion analysis, DNA sequences necessary to initiate POL1 transcription at the proper sites have also been identified.
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  • 58
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    Current genetics 21 (1992), S. 191-196 
    ISSN: 1432-0983
    Keywords: Continuous culture ; Amino acid analogs ; Overproducer yeast mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants resistant to ethionine, a toxic analog of methionine, were selected by subjecting yeast cells to competition experiments under continous culture, controlled by pH, with a wide range of increasing ethionine concentrations. The mutants accumulated up to over 30 mM methionine and were able to grow in ethionine concentrations from 0.5 to 50 mM, whereas the wild-type strain stopped growing at 0.1 mM ethionine, and its free methionine pool was 0.2 mM. From ethionine-resistant mutants, strains able to overproduce threonine were isolated by selecting either in continuous or in batch cultures, the latter supplemented with 0.1–5 mM hydroxynorvaline a toxic analog of threonine. These mutants accumulated up to over 200 mM of threonine (the internal pool of threonine in the wild-type was around 5 mM), grew in minimal medium with growth rates similar to that of the wild-type, accumulated the analogs at internal concentrations proportional to the external, and accumulated other amino acids such as homoserine, aspartate, isoleucine and S-adenosyl-methionine.
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  • 59
    ISSN: 1432-0983
    Keywords: Yeast ; Galactokinase ; Mutant selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The galactose analogue 2-deoxy-galactose (2DG) has been widely used to select for mutations in the gene encoding the galactose pathway enzyme galactokinase (GalK). We have tested the effect of 2DG on Candida albicans to see if it could be used to obtain GalK- mutants in this diploid asexual yeast. 2DG was shown to be toxic to wild-type cells. Enzyme assays demonstrated that 2DG can induce GalK as efficiently as galactose. Examination of the initital rate of galactose uptake indicated that the galactose transport system is constitutive. 2DG-resistant mutants were isolated from mutagenized cultures and shown to have very low levels of GalK activity. The potential genetic applications of this system of direct mutant selection are discussed.
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  • 60
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; Gene mapping ; Mitochondrial genome ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report the cloning and physical mapping of the mitochondrial genome of Chlamydomonas eugametos together with a comparison of the overall sequence structure of this DNA with the mitochondrial genome of Chlamydomonas moewusii, its closely related and interfertile relative. The C. eugametos mitochondrial DNA (mtDNA) has a 24 kb circular map and is thus 2 kb larger than the 22 kb circular mitochondrial genome of C. moewusii. Restriction mapping and heterologous fragment hybridization experiments indicate that the C. eugametos and C. moewusii mtDNAs are colinear. Nine cross-hybridizing restriction fragments common to the C. eugametos and C. moewusii mtDNAs, and spanning the entirety of these genomes, show length differences between homologous fragments which vary from 0.1 to 2.3 kb. A 600 bp subfragment of C. moewusii mtDNA, within one of these conserved fragments, showed no hybridization with the C. eugametos mtDNA. Of the 73 restriction sites identified in the C. eugametos and C. moewusii mtDNAs, five are specific to C. moewusii, eight are specific to C. eugametos and 30 are common to both species. Hybridization experiments with gene probes derived from protein-coding and ribosomal RNA-coding regions of wheat and Chlamydomonas reinhardtii mtDNAs support the view that the small and large subunit ribosomal RNA-coding regions of the C. eugametos and C. moewusii mtDNAs are interrupted and interspersed with each other and with protein-coding regions, as are the ribosomal RNA-coding regions of C. reinhardtii mtDNA; however, the specific arrangement of these coding elements in the C. eugametos and C. moewusii mtDNAs appears different from that of C. reinhardtii mtDNA.
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  • 61