Nitrogen Starvation-induced Phosphorylation of Ras1 Protein and Its Potential Role in Nutrient Signaling and Stress Response.

Ras1 is a small GTPase in the budding yeast Saccharomyces cerevisiae that regulates nutrient signaling. It has been shown that Ras1 undergoes phosphorylation, but the functional consequences and regulation of Ras1 phosphorylation remain unknown. Here we identify Ser-226 as an important residue for Ras1 phosphorylation, as mutating this residue to an alanine drastically diminishes the level of Ras1 phosphorylation. Notably, phosphorylated Ras1 accumulates as the cells approach the stationary phase of growth. Likewise, subjecting cells to nitrogen starvation also elevates the level of Ras1 phosphorylation. Interestingly, blocking Ras1 phosphorylation diminishes the level of autophagy and also renders the cells more sensitive to heat shock. Together, these data suggest a role of Ras1 phosphorylation in modulating nutrient signaling and stress response.