Two-ended recombination at a Flp-nickase-broken replication fork

作者：Rajula Elango, Namrata M. Nilavar, Andrew G. Li, Daniel Nguyen, Emilie Rass, Erin E. Duffey, Yuning Jiang, Abdulkadir Abakir, Nicholas A. Willis, Jonathan Houseley, Ralph Scully · 发表于：Molecular Cell · 年份：2024 · DOI：10.1016/j.molcel.2024.11.006 · 被引用次数：28 · 研究领域：DNA Repair Mechanisms、CRISPR and Genetic Engineering、Mitochondrial Function and Pathology

Replication fork collision with a DNA nick can generate a one-ended break, fostering genomic instability. The opposing fork's collision with the nick could form a second DNA end, enabling conservative repair by homologous recombination (HR). To study mechanisms of nickase-induced HR, we developed the Flp recombinase "step arrest" nickase in mammalian cells. A Flp-nick induces two-ended, BRCA2/RAD51-dependent short tract gene conversion (STGC), BRCA2/RAD51-independent long tract gene conversion, and discoordinated two-ended invasions. HR pathways induced by a replication-independent break and the Flp-nickase differ in their dependence on BRCA1, MRE11, and CtIP. To determine the origin of the second DNA end during Flp-nickase-induced STGC, we blocked the opposing fork using a Tus/Ter replication fork barrier (RFB). Flp-nickase-induced STGC remained robust and two ended. Thus, a single replication fork's collision with a Flp-nick triggers two-ended HR, possibly reflecting replicative bypass of lagging strand nicks. This response may limit genomic instability during replication of nicked DNA.