DNA replication is a complex and highly regulated cellular process that ensures faithful duplication of the entire genome. To prevent genomic instability, several additional processes are coordinated with DNA replication. Eukaryotic cells employ a conserved surveillance mechanism called the S-phase checkpoint to activate a phosphorylation cascade while encountering DNA damage during DNA replication. In addition, DNA replication must also coordinate with sister chromatid cohesion, so that sister DNAs emerged from the forks are physically connected until chromosomal segregation takes place. Mcm2-7, the eukaryotic replicative helicase that unwinds dsDNA and positions at the vanguard of the replication fork, is likely the commonality among these cellular processes. In my thesis work, I find that ATP hydrolysis in one specific active site (Mcm6/2) is required to mediate DNA replication checkpoint response, sister chromatid cohesion and DNA replication initiation. Further examination reveals that a subcircuit of the checkpoint pathway including MEC1 and MRC1 and ends with Mcm2-7 is required to mediate sister chromatid cohesion. Finally, misregulation of these processes causes genomic instability and likely missegregation of chromosomes. My findings lead to a model that the regulation of ATP hydrolysis at the Mcm6/2 active site by Mrc1 modulates Mcm2/5 gate open and gate closure during initiation, DNA damage and sister chromatid cohesion
