Xenopus Mcm10 binds to origins of DNA replication after Mcm2-7 and stimulates origin binding of Cdc45.

Current models suggest that the replication initiation factor Mcm10 is required for association of Mcm2-7 with origins of replication to generate the prereplicative complex (pre-RC). Here we report that Xenopus Mcm10 (XMcm10) is not required for origin binding of XMcm2-7. Instead, the chromatin binding of XMcm10 at the onset of DNA replication requires chromatin-bound XMcm2-7, and it is independent of Cdk2 and Cdc7. In the absence of XMcm10, XCdc45 binding, XRPA binding, and initiation-dependent plasmid supercoiling are blocked. Therefore, XMcm10 performs its function after pre-RC assembly and before origin unwinding. As one of the earliest known pre-RC activation steps, chromatin binding of XMcm10 is an attractive target for regulation by cell cycle checkpoints.