A novel ring-like complex ofXenopusproteins essential for the initiation of DNA replication

Abstract

We have identifiedXenopushomologs of the budding yeast Sld5 and its three interacting proteins. These form a novel complex essential for the initiation of DNA replication inXenopusegg extracts. The complex binds to chromatin in a manner dependent on replication licensing and S-phase CDK. The chromatin binding of the complex and that of Cdc45 are mutually dependent and both bindings requireXenopusCut5, the yeast homolog of which interacts with Sld5. On replicating chromatin the complex interacts with Cdc45 and MCM, putative components of replication machinery. Electron microscopy further reveals that the complex has a ring-like structure. These results suggest that the complex plays an essential role in the elongation stage of DNA replication as well as the initiation stage.