Mcm10 is a conserved eukaryotic DNA replication factor whose function has remained elusive. We report here that Mcm10 binding to replication origins in budding yeast is cell cycle regulated and dependent on the putative helicase, Mcm2-7. Mcm10 is also an essential component of the replication fork. A fraction of Mcm10 binds to DNA, as shown by histone association assays that allow for the study of chromatin binding in vivo. However, Mcm10 is also required to maintain steady-state levels of DNA polymerase-alpha (polalpha). In temperature-sensitive mcm10-td mutants, depletion of Mcm10 during S phase results in degradation of the catalytic subunit of polalpha, without affecting other fork components such as Cdc45. We propose that Mcm10 stabilizes polalpha and recruits the complex to replication origins. During elongation, Mcm10 is required for the presence of polalpha at replication forks and may coordinate DNA synthesis with DNA unwinding by the Mcm2-7 complex.
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