Cell-cycle progression is monitored by checkpoint pathways that pause the cell cycle when stress arises to threaten the integrity of the genome. Although activation of checkpoint pathways has been extensively studied, our understanding of how cells resume the cell cycle when the stress is resolved is relatively limited. In this study, we identify the Saccharomyces cerevisiae F-box protein Dia2 as a novel player in the S-phase checkpoint recovery pathway. Dia2 is required for robust deactivation of the Rad53 checkpoint kinase and timely completion of DNA replication during recovery from DNA damage induced by methyl methanesulfonate (MMS). Aiming to identify the substrate of SCF(Dia2) (Skp1/Cul1/F-box Dia2) in checkpoint recovery, we performed a genetic screen to identify suppressors of dia2Δ cells. The screen identified a new checkpoint-defective allele of MRC1 truncated at the C terminus. We found that checkpoint-defective mrc1 alleles suppress the MMS sensitivity and the checkpoint recovery defect of dia2Δ cells. In addition, Dia2 contributes to Mrc1 degradation during S-phase checkpoint recovery. Furthermore, induced degradation of checkpoint-functional Mrc1 partially rescues the checkpoint recovery defect of dia2Δ cells. We propose a model in which Dia2 mediates Mrc1 degradation to help cells resume the cell cycle during recovery from MMS-induced DNA damage in S-phase.
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