GENETIC CONTROL OF NUTRITIONAL STARVATION IN YEAST

实验旨在确定酿酒酵母中倍性控制基因表达的机制。这项工作对人类细胞的异常生长有意义，因为细胞控制异常的肿瘤细胞通常含有异常数量的染色体。虽然超倍体通常被认为是细胞周期控制异常的结果，但这一建议表明，超倍体本身可能导致细胞增殖所需的关键分子的异常表达。基因阵列将被用来确定在单倍体和四倍体之间倍性不同的同基因酵母菌株中基因转录倍性控制的分子基础。其中一组实验旨在确定G1期细胞周期蛋白转录在倍性控制细胞大小和细胞增殖中的作用。这些研究将确定倍性控制本身是否受细胞周期的调控。由于多倍体细胞比整倍体细胞对营养饥饿更加敏感，导致整倍体和多倍体生长控制差异的基因将被识别出来。交配型基因座上的杂合性和染色体配对在多倍体对营养饥饿的反应中的作用将被确定。已知的倍性控制基因之一的启动子将被分析，以确定对倍性控制做出反应的顺式作用序列。另一个屏幕被设计用来识别介导倍性控制的反式作用基因。耐盐性是一种倍性敏感的表型，将被用来筛选倍性依赖表型的抑制因子。此外，还将阐明盐敏感性的细胞学基础。第三组实验确定了RIM1转录因子在稳定期代谢中的作用。该酵母同系物是一种已知的青霉素生产真菌调节剂，被建议用于控制酵母菌的固定相代谢。第四组实验侧重于敌草胺的作用，这是一种保守的延伸因子2在细胞调节中的翻译后修饰。DPH突变体的静止相缺陷在二倍体中比在单倍体中更严重。所提出的实验将有助于更深入地理解倍性在异常细胞增殖中的作用。

Experiments are designed to determine the mechanism by which gene expression is controlled by ploidy in the yeast Saccharomyces cerevisiae. This work has implications for abnormal cell growth in humans because tumor cells with aberrant cell control often contain an abnormal number of chromosomes. Although hyperploidy is usually viewed as a consequence of aberrant cell cycle control, this proposal suggests that hyperploidy itself may cause the abnormal expression of key molecules required for cell proliferation. Gene arrays will be used to determine the molecular basis for the ploidy control of gene transcription in isogenic yeast strains whose ploidy varies from haploid to tetraploid. One set of experiments is designed to identify the role of G1 cyclin transcription in the ploidy control of cell size and cell proliferation. These studies will determine whether ploidy control is itself cell cycle regulated. As polyploid cells are much more sensitive to nutritional starvation that their euploid counterparts, the genes responsible for the differences in euploid and polyploid growth control will be identified. The role of heterozygosity at the mating type locus and chromosome pairing in the response of polyploids to nutritional starvation will be ascertained. The promoter of one of the genes known to be transcriptionally controlled by ploidy will be analyzed to identify cis-acting sequences that respond to ploidy control. Another screen is designed to identify the trans-acting genes that mediate ploidy control. Salt resistance, a ploidy sensitive phenotype, will be used to screen for suppressors of the ploidy dependent phenotype. In addition the cellular basis for salt sensitivity will be elucidated. A third set of experiments identifies the role of the Rim1 transcription factor in stationary phase metabolism. This yeast homolog of a known fungal regulator of penicillin production is proposed to control stationary phase metabolism in Saccharomyces. A fourth set of experiments focuses on the role of dipthamide, a conserved posttranslational modification of elongation factor2 in cellular regulation. dph mutants have a stationary phase defect that is again more severe in diploids that in haploids. The experiments proposed will lead to a deeper understanding of the role of ploidy in aberrant cell proliferation.