RAD51 -Dependent Break-Induced Replication Differs in Kinetics and Checkpoint Responses from RAD51 -Mediated Gene Conversion

Abstract

ABSTRACT Diploid Saccharomyces cells experiencing a double-strand break (DSB) on one homologous chromosome repair the break by RAD51 -mediated gene conversion >98% of the time. However, when extensive homologous sequences are restricted to one side of the DSB, repair can occur by both RAD51 -dependent and RAD51 -independent break-induced replication (BIR) mechanisms. Here we characterize the kinetics and checkpoint dependence of RAD51 -dependent BIR when the DSB is created within a chromosome. Gene conversion products appear within 2 h, and there is little, if any, induction of the DNA damage checkpoint; however, RAD51 -dependent BIR occurs with a further delay of 2 to 4 h and cells arrest in response to the G 2 /M DNA damage checkpoint. RAD51 -dependent BIR does not require special facilitating sequences that are required for a less efficient RAD51 -independent process. RAD51 -dependent BIR occurs efficiently in G 2 -arrested cells. Once repair is initiated, the rate of repair replication during BIR is comparable to that of normal DNA replication, as copying of >100 kb is completed less than 30 min after repair DNA synthesis is detected close to the DSB.