Systematic Characterization of Donor Preference and Stress Response Mechanisms in Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae, or the baker's yeast, is an ideal model organism for biological studies, allowing for easy manipulation, and thus systematic characterization of different biological phenomena and their underlying genetic mechanisms. Here, I have leveraged such characteristic features of S. cerevisiae for developing experimental platforms which can be used towards understanding two fundamental biological processes: "DNA recombination" and "The cellular response to environmental cues". DNA damage is the major cause of cancer, and the target for many anticancer therapies. The DNA repair capability of a cell is essential for maintaining the integrity of its genome and influences the life span of the organism. Deficiency in DNA repair pathways leads to cell senescence, apoptosis, or formation of a cancerous tumor. Mating-type switching in S. cerevisiae, which arises from a similar double-strand break-induced gene conversion event, has traditionally been studied for understanding the mechanism of DNA repair and recombination. Here we have focused on donor preference, an aspect of mating type switching which is not fully understood and explored yet. In a separate endeavor towards system-level characterization of complex biological phenotypes in S. cerevisiae, we focused on yeast's response to environmental perturbations and signals. To that end, I picked two members of the signal transduction pathways involved in responding to environmental changes: Cdc19 and Msn2. Cdc19 is the main pyruvate kinase isozyme which is phosphorylated in response to glucose depletion. Msn2 transcription factor modulates cell's response to several types of stress at the transcriptome level. We found that while the phosphorylation state of yeast pyruvate kinase is modified in response to glucose availability, its activity is controlled by ultrasensitive allostery. Phosphorylation of Msn2 on the other hand has a more robust role in regulation of its activity. We found new phosphosites on Msn2 and showed that their level of phosphorylation changes upon environmental perturbations