Epigenetic inheritance in Saccharomyces cerevisiae: the competition between CAF-I and Rrm3p for the DNA sliding clamp PCNA
Conversions between two epigenetically heritable states (fully active or silent) are regulated by chromatin and integral for development and disease. The mechanisms of epigenetic conversions are not fully elucidated. CAF-I and Rrm3p are key regulators of conversions. I hypothesized that the kinases Cdc7p and Cdc28p phosphorylate CAF-I and facilitate its association with PCNA. Both CAF-I and Rrm3p interact with PCNA through the same domain. Therefore, I hypothesized that CAF-I and Rrm3p compete for PCNA. I used a modified yeast two-hybrid assay to assess the CAF-I/PCNA interaction. This interaction was significantly reduced when Cdc7p phosphorylation of Cac1p is prevented. I used a similar assay to show that CAF-I and Rrm3p compete for PCNA. I also showed differential binding between Cac1p and Rrm3p, which indicated that the PIP box is not the only motif responsible for the interaction. Finally, I proposed and discussed a new model for such conversions.