Protein Kinase Inhibition in G2 Causes Mammalian Mcm Proteins to Reassociate with Chromatin and Restores Ability to Replicate

Intact nuclei from G2-phase mammalian cells will replicate their DNA inXenopusegg extract if they are preexposed to the protein kinase inhibitor 6-dimethylaminopurinein vivo(Coverleyet al., Exp. Cell Res.225, 294–300, 1996). Here, we demonstrate that this competence to rereplicate is accompanied by alterations in the subcellular distribution of the Mcm family of proteins, which are implicated in replication licensing (Hennessyet al., Genes Dev.4, 2252–2263, 1990; Kubotaet al., Cell81, 601–609, 1995; and Chonget al., Nature375, 418–421, 1995). All family members reassociate with chromatin in G2 cells and this correlates closely with regeneration of replication competence. Moreover, newly bound Mcm proteins are functional for replication because, unlike untreated G2 nuclei, replication of treated G2 nucleiin vitrooccurs independent of theXenopusMcm protein complex. These observations show that the postreplicative state is actively maintained in G2 cells by a protein kinase(s) which regulates the behavior of Mcm family proteins.