Potent DNA strand annealing activity associated with mouse Mcm2?7 heterohexameric complex.

ABSTRACT: Mini-chromosome maintenance (Mcm) is a central component for DNA unwinding reaction during eukaryotic DNA replication. Mcm2?7, each containing a conserved ATPase motif, form a six subunit-heterohexamer. Although the reconstituted Mcm2?7-Cdc45-GINS (CMG) complex displays DNA unwinding activity, the Mcm2?7 complex does not generally exhibit helicase activity under a normal assay condition. We detected a strong DNA strand annealing activity in the purified mouse Mcm2?7 heterohexamer, which promotes rapid reassociation of displaced complementary single-stranded DNAs, suggesting a potential cause for its inability to exhibit DNA helicase activity. Indeed, DNA unwinding activity of Mcm2?7 could be detected in the presence of a single-stranded DNA that is complementary to the displaced strand, which would prevent its reannealing to the template. ATPase-deficient mutations in Mcm2, 4, 5 and 6 subunits inactivated the annealing activity, while those in Mcm2 and 5 subunits alone did not. The annealing activity of Mcm2?7 does not require Mg2+ and ATP, and is adversely inhibited by the presence of high concentration of Mg2+ and ATP while activated by similar concentrations of ADP. Our findings show that the DNA helicase activity of Mcm2?7 may be masked by its unexpectedly strong annealing activity, and suggest potential physiological roles of strand annealing activity of Mcm during replication stress responses.

SUBMITTER: You Z 

PROVIDER: S-EPMC5499727 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature