Chromatin loading of Smc5/6 is induced by DNA replication but not by DNA double-strand breaks.

Smc6, a member of the structural maintenance of chromosomes (SMC) family of proteins, forms a complex with related Smc5. Genetic analyses of yeast have demonstrated the involvement of Smc6 in DNA repair and checkpoint responses. In this study, we investigated the role of the Smc5/6 complex in higher eukaryotes by analyzing its behavior in Xenopus laevis egg extracts. Smc5/6 was loaded onto chromatin during DNA replication in a manner dependent on the initiation of DNA synthesis, and it dissociated from chromatin during mitosis. Moreover, the induction of DNA double-strand breaks following replication did not significantly affect the amount of chromatin-associated Smc6. These findings suggest that the Smc5/6 complex is regulated during the cell cycle, presumably in anticipation of DNA damage that may arise during replication.