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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Site-specific recombinases of the resolvase and DNA invertase family all contain a tyrosine residue close to the N-terminus, and four residues away from a serine that has been implicated in catalysis of DNA strand breakage and reunion. To examine the role of this tyrosine in recombination, we have constructed a mutant of γδ resolvase in which the tyrosine (residue 6) is replaced by phenytalanine. Characterization of the Y6F mutant protein in vitro indicated that although it was highly defective in recombination, it could cleave ONA at the cross-over site, form a covalent resolvase-DNA complex and rejoin the cleaved cross-over site (usually restoring the parental site). These data rule out a direct role of the Tyr-6 hydroxyl as the nucleophile In the DNA cleavage reaction and strengthen the conclusion that this nucleophile is the nearby invariant serine residue, Ser-10. We conclude that Tyr-6 is essential for fully coordinated strand cleavage and exchange, but is dispensable for individual strand cleavage and religation reactions.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 74 (1996), S. 209-223 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Experimental results suggest that neurons in the cortex synchronize their action potentials on the millisecond time scale. More importantly this binding expresses functional relationships between the neurons. A model of neuronal interactions is proposed in which simultaneous discharges of neurons develop through specialized synaptic circuits. As an important prerequisite for this synchronization it is demonstrated that SynFire chains, generating different levels of excitation, propagate their activity waves at distinct velocities. Two chains were coupled by excitatory synapses and their activity was initiated at different times. Due to synaptic interactions, activity in the earlier-initiated chain accelerates propagation in the other chain until the two activity waves are synchronized. Compared with several neural network models with oscillatory units, physiologically more plausible neurons are simulated. It is still under debate whether neurons in the cortex show oscillatory dischargesper se. In particular, a high rate of noise relative to very weak synaptic gains cannot impair our results in the neural network simulations.
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  • 3
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
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  • 4
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Hereditary neuralgic amyotrophy (HNA) is a rare autosomal dominant disorder on chromosome 17q, associated with recurrent, episodic, painful brachial plexus neuropathy. Dysmorphic features, including hypotelorism, long nasal bridge and facial asymmetry, are frequently associated with HNA. To assess genetic homogeneity, determine the cytogenetic location, and identify flanking markers for the HNA locus, six pedigrees were studied with multiple DNA markers from distal chromosome 17q. The results in all pedigrees supported linkage of the HNA locus to chromosome 17. A maximum combined lod score (Ζ = 10.94, £ = 0.05) was obtained with marker D17S939 and the maximum multipoint lod score was 22.768 in the interval defined by D17S802– D17S939. An analysis of crossovers placed the HNA locus within an approximate 4.0-cM interval flanked by D17S1603 and D17S802. Analysis of DNA from a human/mouse somatic cell hybrid with linked markers suggests that band 17q25 harbors the HNA locus. These results support genetic homogeneity within HNA and define a specific interval and a precise cytogenetic location in chromosome 17q25 for this disorder.
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  • 5
    ISSN: 1433-0407
    Keywords: Schlüsselwörter Multiple Sklerose ; Immunpathogenese ; Therapie ; Key words Multiple sclerosis ; Immunopathogenesis ; Therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Extensive research in the field of multiple sclerosis (MS) has lead to a preliminary pathogenetic concept without solving the etiopathogenesis. According to animal experiments and human in vitro studies MS is a T cell-mediated autoimmune disease. Experimental therapeutical strategies are aiming at the inhibition of T cell activation, transmigration through the blood brain barrier and local inflammation and demyelination. Several substances are already being tested in clinical studies with magnetic resonance imaging as a tool to quantify inflammatory lesions and to shorten the study course. This review will give a summary about actual experimental therapies resulting from the current pathogenetic concept.
    Notes: Zusammenfassung Eingehende Forschung auf dem Gebiet der multiplen Sklerose (MS) konnte die Ätiopathogenese der Erkrankung nicht aufklären, hat jedoch zu der Erstellung eines vorläufigen pathogenetischen Konzepts geführt. Tierexperimentelle Daten und Ergebnisse aus humanen In-vitro-Untersuchungen sprechen dafür, daß die MS eine T-Zell-vermittelte Autoimmunerkrankung ist. Es gibt eine Reihe von experimentellen Therapiestrategien, die in die T-Zellaktivierung eingreifen, im Bereich der Blut-Hirn-Schranke intervenieren oder lokale Entzündungs- und Entmarkungsprozesse hemmen. Die Therapien, die sich auf den Menschen übertragen lassen, befinden sich teilweise bereits in der klinischen Erprobung. Dabei wird die Prüfung durch die Möglichkeit, Entzündungsaktivität im ZNS kernspintomographisch sichtbar zu machen und zu quantifizieren, deutlich verkürzt und vereinfacht. Ziel dieser Übersicht ist eine Zusammenstellung der spezifischen immuntherapeutischen Ansätze, die sich aus den bisherigen pathogenetischen Erkenntnissen ergeben.
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  • 6
    ISSN: 1432-2242
    Keywords: Key words Barley ; Haploids ; Two-row ; Six-row ; Quantitative trait loci
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A study was conducted on a two-row/six-row cross of barley to (1) determine the yield potential, (2) detect epistasis and genetic correlations, (3) estimate the heritabilities of six agronomic traits, and (4) study the effect of the V locus on the agronomic traits in the barley cross. The effects of five other marker loci (Re2, s, R, Est1, and Est5) on the six agronomic traits were also studied. One hundred and ninety doubled-haploid (DH) lines were derived from a ‘Leger’/CI9831 cross using the bulbosum method. The DH lines and the two parents were tested for grain yield, test weight, seed weight, plant height, lodging, and heading/maturity at two locations in Eastern Canada in 1993. Additive×additive epistasis and genetic correlations were detected for some of the agronomic traits. Many of the heritability estimates were high; however, significant progress in yield improvement would be difficult to achieve because of a low mean yield of the DH lines. Under the growing conditions in Eastern Canada, six-row lines outyielded two-row by 20–27%. Six-row lines, however, were associated with low test weight, low seed weight, and severe lodging. Some two-row lines yielded higher than the two-row parent CI9831, but none of the six-row lines yielded higher than the six-row parent ‘Leger’. The R, s, and Est5 loci were associated with the six agronomic traits, but the Est1 locus was apparently not associated with the agronomic traits. The effect of the Re2 locus was probably due to its close linkage with the V locus. Further studies are needed to determine if superior six-row lines can be developed from two-row/six-row crosses.
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  • 7
    ISSN: 1433-0407
    Keywords: Schlüsselwörter Nebenwirkungen ; Kortikoide ; Key words Side effects ; Steroids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Many side effects of steroid treatment have been reported. Even experienced neurologists may not know all important side effects to the nervous system. Autonomic nervous system dysfunction, psychosis and myopathy are more frequently encountered than dependency, reversible dementia, brain atrophy and benign intracranial hypertension. This review describes symptomatology, pathogenesis and treatment of these steroid-induced side effects.
    Notes: Zusammenfassung Über eine Vielzahl von Nebenwirkungen der Therapie mit Kortikoiden ist berichtet worden. Wichtige Nebenwirkungen auf das Nervensystem sind auch erfahrenen Neurologen nicht immer bekannt. Neben den häufig auftretenden unerwünschten Wirkungen wie vegetativen Störungen, Psychosen und Myopathien finden sich seltene wie Abhängigkeit, dementielle Entwicklung, Hirnatrophie und Pseudotumor cerebri. Diese Übersicht beschreibt Symptomatologie, Pathogenese und Behandlung dieser kortikoidinduzierten Nebenwirkungen.
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  • 8
    ISSN: 1432-0533
    Keywords: Glioma ; Stem cell factor ; Oncogene ; Kit Autocrine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Stem cell factor (SCF), a hematopoietic growth factor, is the ligand of the tyrosine kinase receptor encoded by the c-kit proto-oncogene. Beside the important role of this receptor-ligand complex in hematopoiesis, gametogenesis and melanogenesis, SCF and its receptor have been shown to be expressed in the brain. We have studied the expression of SCF and c-kit in 20 human malignant glioma cell lines at the mRNA as well as at the protein level. In addition, recombinant human (rh) SCF was tested in [3H]thymidine uptake assays for a mitogenic effect on these cells. SCF and c-Kit proteins were detected in the cytoplasm of glioma cells by alkaline phoshatase-monoclonal anti-alkaline phosphatase immunostaining and Western blot analysis. However, neither SCF nor c-Kit were seen on the cell surface by flow cytometry. Furthermore, none of the proliferation assays showed a mitogenic effect for exogenously added rhSCF. Blocking studies using an anti-SCF antibody failed to demonstrate modulating effects on the growth of selected cell lines. These results suggest that SCF and c-Kit may mediate non-proliferative signals or may employ intracellular mechanisms for autocrine growth regulation of glioma cells.
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  • 9
    ISSN: 1432-041X
    Keywords: Key words Hydrozoa ; Hydra ; RACK1 ; WD-repeat proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A gene encoding a member of the growing family of regulatory WD-repeat proteins has been identified in Hydra vulgaris. About 80% of its deduced amino acids are identical to RACK1, which has recently been identified in rat as a receptor for activated C kinase. The presence of a consensus sequence believed to be important for interaction with protein kinase C, prompted us to term the new sequence HvRACK1 (Hydra vulgaris RACK1). In situ hybridization revealed an abundant message restricted to 80% of the body column with the strongest signal in the upper body half. Terminally differentiated structures (foot, tentacles and apicalmost hypostomal cells) were completely free of expression. A corresponding prepattern was established in bisected animals at least 10 h before the regenerating structure began to form. In normal animals HvRACK1 transcripts were contained mainly in interstitial cells (i-cells), gland cells and digestive epithelial cells. Depletion of i-cells and their derivatives by hydroxyurea (HU) treatment induced expression of the gene in epithelio-muscular and -digestive cells with the overall expression level remaining stable as confirmed by northern blotting. Polyps consisting almost exclusively of epithelial cells expressed HvRACK1 differentially along the body axis with a maximum in the head (except tentacles and the apicalmost ectoderm of the hypostome) and fading out towards the foot. The enhanced expression level in epithelial cells of HU-treated animals indicates that these might take over regionspecific HvRACK1 functions usually inherent to interstitial cells and certain derivatives of this lineage.
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  • 10
    ISSN: 0392-6737
    Keywords: Optical properties of thin films, surfaces, and layer structures (superlattices, heterojunctions, and multilayers)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The development of multilayer optics has profound implications for soft-X-ray/UV astronomy, since it allows to extend the use of normal-incidence telescopes to cover the XUV region where lines are formed at greatly different temperatures (105–107 K). A multilayer mirror consists of alternating thin layers of suitable materials deposited on a substrate and its performance depends not only on the optical properties of the materials but also on the design of the multilayer. In this study we have computed the reflectivity of multilayer mirrors to select both the materials and the multilayers design to achieve the best performance in the wavelength range from 30 to 350 Å. Our calculations show that high theoretical reflectivities, from 0.2 to 0.8 and relatively narrow bandpasses, from ∼ 1Å to ∼30 Å, can be obtained, in the wavelength range from 30 to 350 Å, by a suitable choice of the materials and of the multilayer design.
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