Dynamic switching between regression and recovery modes of replication fork by single Werner syndrome protein complex

Abstract

Numerous DNA damages cause stalling of DNA replication, which need to be properly processed for maintaining genome integrity. Regression of stalled replication fork, which is driven by ATP-consuming molecular motors, is a required step for repairing the stalled replication fork. Due to the transient nature of this process, however, many critical questions are still remaining unanswered. Here we developed single-molecule FRET assays to monitor the regression of model replication fork by WRN. As a result, we revealed that single WRN complex is a bidirectional motor which can perform both regression and recovery of replication forks. We also found that nick, gap, and mismatches can hinder the fork regression. ATP hydrolysis is required for both activation and progression of fork regression, but activation step was the rate-limiting step. We also observed that if the WRN is activated, the rate of regression is about 3bp/s.