Mms1 and Mms22 are important mediators of genome stability in Saccharomyces cerevisiae. Deletion mutants of both genes display decreased viability in the presence of a number of known DNA damaging agents as well as agents that perturb DNA replication. Here I present a detailed analysis of Mms1 and Mms22 function in stabilizing DNA replication forks. I find that mms1∆ and mms22∆ strains accumulate spontaneous DNA damage and have an increased rate of mutation during a normal cell cycle. Additionally, treatment with genotoxic agents causes defects in induced recombination as well as inhibiting the ability of cells to efficiently recover from DNA damage. Genetic interaction data support a model where Mms1 and Mms22 function with components of the replication fork. Accordingly I observed that the enrichment of key replication fork proteins at regions proximal to replication origins is decreased in mms1∆ and mms22∆ cells during replication stress. Furthermore, I monitored DNA replication in wild-type and mms1∆ strains and found that mms1∆ strains exhibit irregular fork progression under conditions of replication stress. I therefore concluded that Mms1 and Mms22 function at replication forks. Lastly, I uncovered that Mms1 is regulated by Rtt101-dependent ubiquitin-mediated proteolysis. Mms1 degradation is likely necessary for its function as overexpression of Mms1 results in decreased cell viability both during a normal cell cycle, and during treatment with DNA damaging agents. I found that Mms1 and Mms22 operate at sites of DNA replication to promote the stability of the genome, especially under conditions of DNA damage and replication fork stress.

Mms1 and Mms22 are important mediators of genome stability in Saccharomyces cerevisiae. Deletion mutants of both genes display decreased viability in the presence of a number of known DNA damaging agents as well as agents that perturb DNA replication. Here I present a detailed analysis of Mms1 and Mms22 function in stabilizing DNA replication forks. I find that mms1∆ and mms22∆ strains accumulate spontaneous DNA damage and have an increased rate of mutation during a normal cell cycle. Additionally, treatment with genotoxic agents causes defects in induced recombination as well as inhibiting the ability of cells to efficiently recover from DNA damage. Genetic interaction data support a model where Mms1 and Mms22 function with components of the replication fork. Accordingly I observed that the enrichment of key replication fork proteins at regions proximal to replication origins is decreased in mms1∆ and mms22∆ cells during replication stress. Furthermore, I monitored DNA replication in wild-type and mms1∆ strains and found that mms1∆ strains exhibit irregular fork progression under conditions of replication stress. I therefore concluded that Mms1 and Mms22 function at replication forks. Lastly, I uncovered that Mms1 is regulated by Rtt101-dependent ubiquitin-mediated proteolysis. Mms1 degradation is likely necessary for its function as overexpression of Mms1 results in decreased cell viability both during a normal cell cycle, and during treatment with DNA damaging agents. I found that Mms1 and Mms22 operate at sites of DNA replication to promote the stability of the genome, especially under conditions of DNA damage and replication fork stress.