Abstract

The application of yeast as a model organism for studying eukaryotic pathways, notably mechanisms and processes of chronological aging, has been recognized for decades. In fact, several signalling pathways of longevity regulation are conserved across phyla; humans (and other mammals) have orthologs and homologs of yeast proteins integrated into these pathways. One of such pathways is the TOR pathway that responds to nutrient levels, notably via TORC1 (a complex with protein kinase activity; contains TOR1 as a core protein). My thesis taps into both of those advantageous properties of Saccharomyces cerevisiae: its ease of culturing for chronological aging studies, and well annotated proteome. I study the chronologically aging quiescent and non-quiescent cell populations under caloric restriction or not using wild-type or tor1 single gene deletion mutant strains. I use quantitative phosphoproteomics – by means of mass spectrometry – to assess the differences and similarities between different cell populations. Caloric restriction has previously been shown to extend the chronological lifespan of yeast and other organisms. Reduced TOR1 activity (such as via inhibitors or by gene deletion) is also shown to extend yeast chronological lifespan in literature. Quiescence, an ability of a nutrient-limited post-mitotic cell to re-enter the cell cycle when the nutrient supply is restored, is also a lifespan-extending process. Combining these factors, I compared the phosphoproteomes of quiescent and non-quiescent yeast cells limited or not limited in calorie supply and having or lacking the TOR1 protein. I found that both the diet and the state of quiescence have significant effect on the phosphorylation of proteins. Moreover, I found that a single-gene-deletion mutation that eliminates the TOR1 protein has a significant impact on both the state of quiescence and the cell phosphoproteome.