Genomic analysis of replication profiles identifies RFCCtf18 as a key mediator of the replication stress response

Maintenance of genome stability during DNA replication depends on surveillance mechanisms that prevent fork collapse and regulate replication timing. To dissect the checkpoint pathways signalling paused forks, we have screened a collection of S. cerevisiae mutants for their ability to activate Rad53, using the repression of late origins as readout for checkpoint efficiency. These genomic data redefine the role of key checkpoint factors. Indeed, they show that DNA damage sensors such as the 9-1-1 clamp and its loader RFCRad24 are unexpectedly dispensable to signal paused forks. In contrast, we found that the alternative clamp loader RFCCtf18 is essential for the Mrc1-dependent activation of Rad53. Moreover, we report that forks collapse in ctf18delta mutants and activate a secondary checkpoint pathway that represses very late origins in a Rad9-dependent manner. We propose a novel and integrated view of the replication checkpoint in which different pathways cooperate to fine tune the cellular response to arrested forks. BrdU-IP from wild-type and 20 mutant yeast cells. Cdc45p IP from 2 yeast strains. Controls (Input DNA) and replicates are included and used to obtain the results files.