Mechanisms preventing Break-Induced Replication during repair of two-ended DNA double-strand breaks

DNA synthesis during homologous recombination (HR) is highly mutagenic and prone to template switches. Two-ended DNA double strand breaks (DSBs) are usually repaired by gene conversion with a short patch of DNA synthesis, thus limiting the mutation load to the vicinity of the DSB. Single-ended DSBs are repaired by Break-Induced Replication (BIR) that involve extensive and mutagenic DNA synthesis spanning even hundreds of kilobases. It remains unknown how mutagenic BIR is suppressed at two-ended DSBs. Here we demonstrate that BIR is suppressed at two-ended DSBs by several proteins coordinating the usage of both DSB ends: ssDNA annealing protein Rad52 and Rad59, D-loop unwinding helicase Mph1, and DSB ends tethering Mre11-Rad50-Xrs2 complex. Finally, BIR is also suppressed when a normally heterochromatic repair template is silenced by Sir2. These findings suggest several mechanisms restricting mutagenic BIR during repair of two-ended DSBs.