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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.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    British journal of dermatology 72 (1960), S. 0 
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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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
    [s.l.] : Nature Publishing Group
    Nature 179 (1957), S. 1252-1253 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The observation of Giaja4 that the gut juice of the snail Helix pomatia dissolves the cell-wall of whole yeasts suggested a basis for an improved method of isolating the yeast protoplast. Following this suggestion, it has been found in these laboratories that the cell-walls of certain strains of ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 178 (1956), S. 1349-1350 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The conclusions of Akabori et al.9 that muscle minces cause a decarboxylative acetoin type of condensation of dihydroxyfumaric acid, leading by way of a hydroxypyruvate intermediate to the formation of tetrose and hexose sugars, led us to re-investigate the action of partially purified yeast ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 178 (1956), S. 1118-1118 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] An aqueous maceration extract of dried Delft baker's yeast was fractionated by precipitation with ammonium sulphate (final concentration 0.65 saturated), dialysis against versene (10-4M disodium ethylenediamine tetraacetate) and removal of interfering impurities by precipitation at pH. 5 and ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 181 (1958), S. 1790-1790 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Formaldehyde, on the other hand, we find reacts quite effectively as an acceptor when pure lithium hydroxypyruvate5 is the donor. The product formed corresponds chromatographically, chemically and enzymicaly with dihydroxyacetone: CH2OH.CO.COOH + H.CHO -〉 CH2OH.CO.CH2OH + CO2 Table 1 shows the ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 193 (1962), S. 256-257 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] MOST of the processes that have been devised for synchronizing division in cultures of microorganisms entail subjecting a population of resting or randomly dividing cells to one or more abrupt environmental changes, for example, in temperature, intensity of illumination or concentration of ...
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