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  • 1
    ISSN: 1432-0983
    Keywords: S. cerevisiae ; Cell cycle ; Suppression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A cell cycle (cdc) mutant of Saccharomyces cerevisiae is described which fails to complement cdc27-1 described by Hartwell et al. 1973), and is designated cdc27–47. Whereas cdc27-1 behaves as a single Mendelian gene (Hartwell et al. 1973), cdc27–47 requires the presence of an additional unlinked gene for expression of temperature-sensitivity. This gene, designated sts47, is present in some, but not all, laboratory wild-type strains. Expression of cdc27-1 is not influenced by STS47. A model for suppression is proposed involving the modification of conformation within a structural or enzyme complex.
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  • 2
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thin layer chromatography on silica gel was used to separate and semiquantitate d-chondrocurarine chloride in d-tubocurarine chloride at the 0.5% to 2% level. This system was also found to separate the o-methylated chondrocurarine iodide and other compounds related to d-tubocurarine chloride.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Log phase cells of Saccharomyces cerevisiae, fully density labelled by growth in 15N medium, were transferred to medium containing only 14N, and DNA replication followed by isopycnic banding in CsCl. Nuclear DNA replicated semi-conservatively, but mitochondrial DNA showed a dispersive pattern, appearing throughout as a single unimodal gradient band the density of which decreased continuously throughout the period of growth. Approaching its first doubling, the mitochondrial component developed marked density heterogeneity, but this was largely dissipated by the time the second doubling was reached. Analysis of single strand densities showed that this phenomenon was an early consequence of a process in which previously incorporated 15N atoms were continually redistributed between old and new DNA strands. By two doublings the operation of this process resulted in the single strands of mitochondrial DNA being indistinguishable in terms of density. The kinetics of density loss of the mitochondrial component showed that incorporation of 15N into mitochondrial DNA following the transfer was negligible and that essentially all pre-incorporated 15N was conserved, indicating the probable absence of metabolic turnover. It was concluded that a primary semi-conservative strand copying step in the replication of mitochondrial DNA is accompanied or closely followed by extensive partial exchanges of homologous strands between duplexes.
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  • 4
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Low concentrations of erythromycin and chloramphenicol (≤0.3 mg/ml) specifically affect intra-mitochondrial protein synthesis in most strains of Saccharomyces cerevisiae, thereby preventing growth on non-fermentable substrates. This effect is reversible, the genetic capacity for respiration in the absence of the drug being unaffected. However, we now show that exposure of growing cells to high concentrations (1.3–3.0 mg/ml) of either antibiotic generates a high frequency of cytoplasmic petite (respiratory-deficient) mutants with a concomitant loss of the cytoplasmic genetic determinant for respiration known as the rho factor. In one strain in which the effect of erythromycin was examined, the entire population abruptly underwent mutation but only after exposure to the drug for several generations. Mitochondrial DNA was synthesised normally during the silent pre-mutational period, but was rapidly lost, by a process partly dependent on degradation, at the time of the mutational event. Intra-mitochondrial protein synthesis was inhibited only about 67% by the lower levels of erythromycin but was completely (99%) inhibited by the higher petite-inducing levels. These results are interpreted as evidence that the normal maintenance of mitochondrial DNA in this organism requires a protein(s) whose assembly in the mitochondria is completely blocked only by high erythromycin concentrations. This protein is normally present in excess and on exposure to high drug levels replication of mitochondrial DNA is unaffected until the supply runs out. When this happens, replication ceases, existing molecules are degraded, and rho factors are destroyed.
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  • 5
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using alkaline sucrose gradients the mechanism of DNA synthesis has been investigated in both log-phase and synchronised cultures of the yeast Saccharomyces cerevisiae. DNA synthesis proceeds via a heterogeneous population of single-stranded intermediates between 7 and 60x106 daltons in size. The size of these molecules and a comparison of their behaviour in log-phase and synchronised cultures suggests they are nascent or completed replicons. The progressive increase in molecular weight of these intermediates during S in synchronous cultures was used as a measure of the rate of DNA synthesis per single strand. During the first half of the period of DNA synthesis in the culture, the observed rate of elongation was 0.82x106 daltons/min. Later in S, an apparent increase in rate was detected, but this may have reflected the joining of completed replicons. In our gradients the pattern of DNA synthesis in the cell cycle mutants cdc2 and 6, thought to make incomplete or faulty DNA at the restrictive temperature (Hartwell, 1974), closely resembled that of the wild-type.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 42 (1988), S. 1029-1032 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Pure iron foils have been implanted with Ti and with Ti plus C and characterized by conversion electron Mössbauer spectroscopy (CEMS) and Auger electron spectroscopy (AES). Both paramagnetic and magnetic phases are observed and attributed to amorphous Fe−Ti−C alloys of differing Ti and C contents. Estimates of the thicknesses of the amorphous layers based on the CEMS data are in good agreement with the AES concentration depth profiles.
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  • 7
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The amorphization of Fe−Zr multilayers due to ion-beam mixing and solid state reaction is studied in detail using the CEMS and CXMS. The nature of the amorphous Fe−Zr phase produced by both processes is the same suggesting that diffusion of Fe is an important mechanism during ion-beam mixing.
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  • 8
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Al x Ga1-xAs semiconductors doped with both natural and enriched119Sn have been studied by Mössbauer spectroscopy (MS) to help to determine the atomic-scale nature of a deleterious, deep-level defect known as the DX center. Spectra have been acquired in the dark at 76 K and under sub-bandgap illumination at 4 or 10 K to distinguish the DX center from the substitutional shallow donor defect. Although electrical differences are clearly detected in these two states, no difference in the Mössbauer spectra are observed. Unexpected high Sn contents, determined by quantitative MS, demonstrate a large non-electrically active Sn fraction in some samples and this may be obscuring the observation of the DX center by both X-ray absorption spectroscopy and MS. Grinding the single-crystal layers into fine powders leads to an Sn defect that is attributed to a surface-oxidized site.
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  • 9
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  As a part of the Atmospheric Model Intercomparison Project (AMIP), the behaviour of 15 general circulation models has been analysed in order to diagnose and compare the ability of the different models in simulating Northern Hemisphere midlatitude atmospheric blocking. In accordance with the established AMIP procedure, the 10-year model integrations were performed using prescribed, time-evolving monthly mean observed SSTs spanning the period January 1979–December 1988. Atmospheric observational data (ECMWF analyses) over the same period have been also used to verify the models results. The models involved in this comparison represent a wide spectrum of model complexity, with different horizontal and vertical resolution, numerical techniques and physical parametrizations, and exhibit large differences in blocking behaviour. Nevertheless, a few common features can be found, such as the general tendency to underestimate both blocking frequency and the average duration of blocks. The problem of the possible relationship between model blocking and model systematic errors has also been assessed, although without resorting to ad-hoc numerical experimentation it is impossible to relate with certainty particular model deficiencies in representing blocking to precise parts of the model formulation.
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  • 10
    ISSN: 1432-1238
    Keywords: Continuous positive airway pressure ; Pulmonary edema ; Hyperearbia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We describe continuous positive airway pressure (CPAP) by mask to reduce hypercarbia in two patients who had pulmonary edema due to congestive heart failure. In such patients, beside reducing venous return and filling pressures, CPAP improves compliance and decreases the work of breathing, thereby improving effective ventilation. Hence, CPAP may be useful to combat not only hypoxemia but also hypercarbia that is associated with pulmonary edema.
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