Cip/Kip proteins that inhibit cyclin dependent kinase 2 (Cdk2) restrain the initiation of DNA replication. Degradation of a Xenopus Kip1 orthologue, Xic1, is dependent on its recruitment to replication origins. This ensures that activation of Cdk2 and subsequent initiation of replication is co-ordinately regulated at, and localized to, replication origins.