Replication Fork Uncoupling Causes Nascent Strand Degradation and Fork Reversal

Abstract

Genotoxic agents can cause nascent strand degradation (NSD) and fork reversal during DNA replication. NSD and fork reversal are crucial biochemical mechanisms that maintain genome stability and they are frequently exploited by chemotherapeutic approaches. However, it is unclear how NSD and fork reversal are triggered. In addition, the fate of the replicative helicase during these processes is unknown. My thesis work has developed a biochemical approach to study synchronous, localized NSD and fork reversal, and validated this approach using cellular experiments. In this study, we show that replication fork uncoupling stimulates NSD of both nascent strands and progressive conversion of uncoupled forks to reversed forks. Importantly, the replicative helicase remains bound during NSD and fork reversal. Unexpectedly, NSD occurs before and after fork reversal, indicating that multiple degradation steps take place. Overall, my dissertation work shows that uncoupling causes NSD and fork reversal and elucidate key events that precede fork reversal.