Abstract
When inappropriate DNA structures arise, they are sensed by DNA structure-dependent checkpoint pathways and subsequently repaired. Recruitment of checkpoint proteins to such structures precedes recruitment of proteins involved in DNA metabolism. Thus, checkpoints can regulate DNA metabolism. We show that fission yeast Rad9, a 9-1-1 heterotrimeric checkpoint clamp component, is phosphorylated by Hsk1Cdc7, the S. pombe Dbf4-Dependent Kinase (DDK) homolog, in response to replication-induced DNA damage. Phosphorylation occurs after 9-1-1 chromatin loading, depends on the Rad9-associated protein Rad4/Cut5TopBP1 and disrupts interactions between Rad9 and RPA. rad9 mutants defective in DDK phosphorylation show wild-type checkpoint responses but abnormal DNA repair protein foci and increased inviability following replication stress. We propose that Rad9 phosphorylation by DDK releases Rad9 from DNA damage sites to facilitate DNA repair.
