Over the last decade, yeast has become a widely used model system to study eukaryotic aging. Two assays have been developed. In the replicative assay, the number of times that one cell can divide and produce daughter cells is defined as its life span. In the chronologic assay, aging is defined as the time a yeast cell can maintain viability in a non-replicative state. While many genes have been reported to affect replicative or chronologic aging in yeast, the difficulty of the assays has precluded a complete assessment of the yeast genome. Further, the relationship between the two yeast assays has not been determined. Through technology development, the use of high throughput machinery and the application of skilled manpower, we will derive quantitative readings for the entire non-essential gene deletion set in both the chronologic (Aim 1) and replicative (Aim 2) aging assays. This analysis will allow us to (1) identify the set of genes that affect either aging assay, (2) compare the two yeast aging assays directly and compare these data sets to a similar aging analysis performed in C. elegans, (3) uncover the mechanisms regulating yeast aging, and (4) identify new pathways that may regulate aging in mammals. A preliminary analysis of the 43 gene deletions or other mutations reported to regulate either yeast chronologic or replicative aging has been completed. In addition, we have now performed a semi-quantitative chronologic aging assay for all (approximately 4900) non-essential yeast gene deletion strains. This analysis has led to the identification of the TOR signaling pathway as a determinant in chronologic aging. Our analysis of replicative aging in these single gene deletion strains, and in strains with multiple deletions, has led to the conclusion that caloric restriction can extend yeast replicative life span by a SIR2-independent, ERC-independent mechanism. 12% of the yeast non-essential gene deletions have been analyzed for replicative life span to date, leading to the identification of 13 new aging genes regulating replicative life span. Prominent among these are genes implicated in TOR signaling and ribosome function. A major focus of Aim 3 will be to characterize this novel pathway to better understand the mechanisms by which caloric restriction delays eukaryotic aging. When completed, this study will dramatically improve our understanding of aging in yeast and lead to models of caloric restriction that can be tested in mammalian systems.
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