LICENSING OF DNA-REPLICATION BY A MULTI-PROTEIN COMPLEX OF MCM P1 PROTEINS IN XENOPUS EGGS/

In eukaryotes, chromosomal DNA is licensed for a single round of repli cation in each cell cycle, Xenopus MCM3 protein has been implicated in the licensing of replication in egg extract. We have cloned cDNAs enc oding five immunologically distinct proteins associated with Xenopus M CM3 as members of the MCM/P1 family, Six Xenopus MCM proteins formed a physical complex in the egg extract, bound to unreplicated chromatin before the formation of nuclei, and apparently displaced from replicat ed chromatin. The requirement of six XMCM proteins for the replication activity of tile egg extract before nuclear formation suggests that t heir re-association with replicated chromatin at the end of the mitoti c cell cycle is a key step for the licensing of replication.