XMCM7, A NOVEL MEMBER OF THE XENOPUS MCM FAMILY, INTERACTS WITH XMCM3AND COLOCALIZES WITH IT THROUGHOUT REPLICATION

A minichromosome maintenance (MCM) protein complex has been implicated in restricting DNA replication to once per cell cycle in Xenopus egg extracts, based on the behavior of a single protein, XMCM3. Using a tw o-hybrid screen with XMCM3, we have identified a novel member of the M CM family in Xenopics that is essential for DNA replication. The prote in shows strong homology to Saccharomyces cerevisiae MCM7 (CDC47) and has thus been named XMCM7. XMCM7 is present in a multiprotein complex with other MCM proteins. It binds to chromatin and is displaced from c hromatin by the act of replication. XMCM7 does not preferentially colo calize with sites of DNA replication but colocalizes with XMCM3 throug hout replication. Immunodepletion of the MCM complex from Xenopus egg extract by anti-XMCM7 antibodies inhibits DNA replication of sperm and permeable HeLa G2 nuclei but not permeable HeLa G1 nuclei. Replicatio n capacity of the Xenopus egg extract immunodepleted of the MCM comple x by anti-XMCM7 antibody can be rescued by MCM proteins eluted from an ti-XMCM3 antibody. We conclude that both proteins are present in the s ame complex in Xenopus egg extract throughout the cell cycle, that the y remain together after binding to chromatin and during DNA replicatio n, and that they perform similar functions.