Direct Observation of Stalled Fork Restart and Lesion Bypass via Fork Regression in the T4 Replication System

Abstract

The restart of a stalled replication fork is a major challenge for DNA replication. Depending upon the nature of the damage, different repair processes might be triggered; one is template switching that is bypass of a leading strand lesion via a Holliday junction formed by fork regression. using Magnetic Tweezers (MT) to study the T4 bacteriophage enzymes, we have reproduced in vitro the complete process of template switching. We show that the UvsW DNA helicase in cooperation with the T4 holoenzyme can overcome leading strand lesion damage by a pseudo stochastic process periodically forming and migrating a four ways Holliday junction. The initiation of the repair process requires partial replisome disassembly via the departure of the replicative helicase.