Rad53 controls DNA unwinding after helicase-polymerase uncoupling at DNA replication forks

Abstract

The coordination of DNA unwinding and synthesis at replication forks promotes efficient and faithful replication of chromosomal DNA. Using the reconstituted budding yeast DNA replication system, we demonstrate that Pol {varepsilon} variants harboring catalytic point mutations in the Pol2 polymerase domain, contrary to Pol2 polymerase domain deletions, inhibit DNA synthesis at replication forks by displacing Pol {delta} from PCNA/primer-template junctions, causing excessive DNA unwinding by the replicative DNA helicase, CMG, uncoupled from DNA synthesis. Mutations that suppress the inhibition of Pol {delta} by Pol {varepsilon} restore viability in Pol2 polymerase point mutant cells. We also observe uninterrupted DNA unwinding at replication forks upon dNTP depletion or chemical inhibition of DNA polymerases, demonstrating that leading strand synthesis is not tightly coupled to DNA unwinding by CMG. Importantly, the Rad53 kinase controls excessive DNA unwinding at replication forks by limiting CMG helicase activity, suggesting a mechanism for fork-stabilization by the replication checkpoint.