Analysis of rho mutability in Saccharomyces cerevisiae

Summary Two additional types of nuclear determinants involved in the control of spontaneous mutability of rho in S. cerevisiae have been identified: mmc and the pet-ts 1, 2, 10, 52 and 53 genes.These genes in their mutated recessive form increase at various extents the number of respiratory deficient cytoplasmic petite mutants accumulated.The gene mmc does not affect the respiratory activity and is not temperature-dependent whereas the pet-ts genes determine at the non permissive temperature a respiratory deficient phenotypes even if they affect the mutability of rho at the permissve and at the non permissive temperature.The data here reported suggest that a replicative complex exists for the mitochondrial DNA.It is in the purpose of this paper to deal with the relative contrition that mmc and pet-ts gene products have in ensuring the fidelity of this replicative complex.     

Calcium and Saccharomyces cerevisiae

The claim that Ca may be a dispensable element for yeast Saccharomyces cerevisiae has been reexamined. The cells of S. cerevisiae could grow in media which contained no added Ca and were deprived of contaminating Ca²⁺ by filtration through a Chelex 100 column. Also, the cells were able to grow in the presence of fairly high concentrations of EGTA. The apparent intracellular concentrations of Ca, assessed from the content of radioactive ⁴⁵Ca in cells preloaded with ⁴⁵CaCl₂, could vary within the range of approx. 2 nM to 2.8 mM, without adversively affecting growth or morphology of the cells. An extremely low affinity for Ca²⁺ of the system taking up Ca into the cells was corroborated. However, even the Chelex 100-treated media were found in contain 1–5 μM Ca when maintained in glass culture vessels. Also, the ability of the cells to take up Ca from a medium containing surplus of EGTA or EDTA was demonstrated. su14CEDTA, alone or in the presence of Ca, could also be transported into the cells. It has been inferred that Ca must be as essential for yeast as it is for other eucaryotic organisms. The omnipresence of contaminating Ca and peculiarities of the Ca transporting system, combined with an intricate intracellular compartmentation of Ca, would account for the impossibility to prove the importance of Ca for yeast by direct growth studies.     

酵母细胞自然衰老分子作用机理的研究进展

衰老是任何生物都无法避免的生理现象,它由多种因素引起,其过程极其复杂.酵母细胞是目前衰老研究领域公认的模式生物,一系列影响衰老的分子作用机理及调控因素的发现均源自于对酵母细胞的研究.自然衰老是酵母细胞的衰老模式之一,由于该衰老过程与其他高等真核细胞(特别是哺乳动物细胞)极为相似,近年来受到广泛关注.全面比较酵母细胞衰老的两种模式,详细介绍自然衰老过程中分子作用机理的研究进展,重点阐述其复杂的自然寿命调控通路,包括卡路里限制以及药物添加对Ras/PKA、Sch9、Tor等营养依赖型调控通路的影响,并展望未来该领域需要解决的重要科学问题,为全面深入了解高等生物,特别是人类自身的衰老机理提供参考.     

Petite-negative mutants of Saccharomyces cerevisiae

Summary A series of yeast mutants has been isolated with the inability to grow on fermentable carbon sources whilst growing normally on ethanol media. One of the mutants, namely MC16/206 lacks pyruvate decarboxylase activity and does not grow on glucose at 37°C but grows on both ethanol and glucose at 27°C. In this strain rho ^- petites are non-viable.     

Regulation of expression of the galactose gene cluster in Saccharomyces cerevisiae

Summary The galactose analogue 2-deoxygalactose was found to inhibit the growth of a mutant strain of Saccharomyces cerevisiae constitutively producing the set of galactose utilization enzymes. Based on this fact, the yeast GAL80 gene negatively regulating the expression of the genes encoding those enzymes was isolated for its ability to confer 2-deoxygalactose resistance on a strain carrying a recessive mutation in that gene. The GAL80 gene was located within a 3.0 kb fragment in the cloned DNA. When the isolated gene was incorporated into a multi-copy plasmid, the induced level of three enzymes encoded by the gene cluster GAL7-GAL10-GAL1 in the host chromosome was lowered. Such a gene dosage effect of GAL80 was further pronounced if sucrose, a sugar causing catabolite repression, was added to the growth medium. The ratio of the enzyme activity of the yeast bearing multiple copies of GAL80 to that of the yeast bearing its single copy significantly varied with the enzyme. From these results we suggest that the intracellular inducer interacts with the GAL80 product and that GAL80 molecules directly bind the GAL cluster genes with an affinity different from one gene to another.The first article of this series is in Mol Gen Genet 191:31–38On a leave absence from Nikka Whisky Co.     

Aluminum-sensitive mutants of Saccharomyces cerevisiae

We are developing budding yeast, Saccharomyces cerevisiae, as a genetic system for the study of tolerance to the trivalent aluminum cation (Al³⁺). We have isolated eight mutants that are more sensitive to Al³⁺ than the wild type. Each mutant represented a different complementation group. A number of the mutants were pleiotropic, and showed defects in other stress responses, changes in tolerance to other metal cations, or abnormal morphology. Two mutants also showed increased dependence on supplemental Mg²⁺ and Ca²⁺. One mutant with a relatively specific sensitivity to Al³⁺ was chosen for molecular complementation. Normal Al³⁺ tolerance was restored by expression of the MAP kinase gene SLT2. Strains carrying deletions of the SLT2 gene, or of the gene for the corresponding MAP kinase–kinase SLK1, showed sensitivity to Al³⁺. These results indicate that the SLT2 MAP kinase signal transduction pathway is required for yeast to sense and respond to Al³⁺ stress. Received: 17 April 1996 / Accepted: 21 October 1996     

出芽酵母Saccharomyces cerevisiae转录抑制因子Rdr1负调控细胞胁迫应答

Rdr1是出芽酵母Saccharomyces cerevisiae的一个转录抑制因子,参与控制细胞的多重药物耐受性,并可能与细胞胁迫应答相关．利用PCR方法扩增RDR1基因片段,将其克隆至高拷贝表达载体pYES2/NTA上并诱导Rdr1蛋白在酵母细胞中过表达．为了揭示转录抑制因子Rdr1在胁迫应答中的作用,比较了RDR1过表达细胞、RDR1缺失突变体细胞和野生型细胞在过氧化氢处理、热胁迫和高盐处理条件下的生长状态,结果显示,RDR1过表达导致细胞对上述3种胁迫作用更敏感,而RDR1缺失则使细胞对这些胁迫作用的耐受性不受影响或有一定增强．为了揭示上述不同细胞在胁迫条件下生长状态的差异与细胞内抗氧化酶活性之间的关系,测定并比较了RDR1过表达细胞、RDR1缺失突变体细胞和野生型细胞中超氧化物岐化酶(superoxide dismutase SOD)、过氧化氢酶、葡萄糖-6-磷酸脱氢酶(glucose-6-phosphate dehydrogenase G6PDH)、谷胱甘肽还原酶(glutathione reductase GR)的活性．结果表明,RDR1缺失突变体细胞具高活性的SOD、过氧化氢酶、G6PDH和GR,而Rdr1过表达细胞中SOD、过氧化氢酶、G6PDH和GR的活性较低．RDR1对SOD和过氧化氢酶活性的影响要大于G6PDH和GR．细胞抗氧化酶活性的变化初步揭示,RDR1过表达细胞对胁迫的敏感和RDR1缺失突变体细胞对胁迫耐受性增加的原因．为转录抑制因子Rdr1在胁迫应答中的负调控作用及其机理提供了初步的遗传学和生物化学证据．     

Mating-type gene switching in Saccharomyces cerevisiae

The study of yeast mating-type (MAT) gene switching has provided insights into several aspects of the regulation of gene expression. MAT switching is accomplished by a highly programmed site-specific homologous recombination event in which mating-type-specific sequences at MAT are replaced by alternative DNA sequences copied from one of two unexpressed donors. The mating-type system has also provided an opportunity to study both the genetic regulation of gene silencing by alterations in chromatin structure, and the basis of preferential recombination between a recipient of genetic information and one of several possible donors.