CRL2(Lrr1) promotes unloading of the vertebrate replisome from chromatin during replication termination

A key event during eukaryotic replication termination is the removal of the CMG helicase from chromatin. CMG unloading involves ubiquitylation of its Mcm7 subunit and the action of the p97 ATPase. Using a proteomic screen in Xenopus egg extracts, we identified factors that are enriched on chromatin when CMG unloading is blocked. This approach identified the E3 ubiquitin ligase CRL2(Lrr1), a specific p97 complex, other potential regulators of termination, and many replisome components. We show that Mcm7 ubiquitylation and CRL2(Lrr1) binding to chromatin are temporally linked and occur only during replication termination. In the absence of CRL2(Lrr1), Mcm7 is not ubiquitylated, CMG unloading is inhibited, and a large subcomplex of the vertebrate replisome that includes DNA Pol ε is retained on DNA. Our data identify CRL2(Lrr1) as a master regulator of replisome disassembly during vertebrate DNA replication termination.