Mitotic CDK promotes replisome disassembly, fork breakage, and complex DNA rearrangements

SUMMARY DNA replication errors generate complex chromosomal rearrangements and thereby contribute to tumorigenesis and other human diseases. Although the events that trigger these errors are not well understood, one candidate is mitotic entry before the completion of DNA replication. To address the impact of mitosis on DNA replication, we employed Xenopus egg extracts. When mitotic CDK (Cyclin B1-CDK1) is used to drive these extracts into mitosis, the E3 ubiquitin ligase TRAIP promotes ubiquitylation of the replicative CMG ( C DC45/ M CM2–7/ G INS) helicase at stalled forks and at forks that have completed DNA synthesis. In both cases, ubiquitylation is followed by CMG extraction from chromatin by the CDC48/p97 ATPase. At stalled forks, CMG removal results in fork breakage and complex end joining events involving deletions and template-switching. Our results identify TRAIP-dependent replisome disassembly as a novel trigger of replication fork collapse and propose it underlies complex DNA rearrangements in mitosis. HIGHLIGHTS TRAIP-dependent MCM7 ubiquitylation removes all CMGs from chromatin in mitosis CMG unloading from stalled forks causes replication fork breakage Replication fork breakage in mitosis causes complex rearrangements New model of replication fork collapse