Cip/Kip proteins that inhibit cyclin dependent kinase 2 (Cdk2) restrain the
initiation of DNA replication. Degradation of a Xenopus Kip1 orthologue, X
ic1, is dependent on its recruitment to replication origins. This ensures t
hat activation of Cdk2 and subsequent initiation of replication is co-ordin
ately regulated at, and localized to, replication origins.