Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.
Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Waltham, MA, USA.
EMBO J. 2021 May 17;40(10):e104847. doi: 10.15252/embj.2020104847. Epub 2021 Apr 12.
DNA synthesis during homologous recombination 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), which involves extensive and mutagenic DNA synthesis spanning up to 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 proteins coordinating the usage of two ends of a DSB: (i) ssDNA annealing proteins Rad52 and Rad59 that promote second end capture, (ii) D-loop unwinding helicase Mph1, and (iii) Mre11-Rad50-Xrs2 complex that promotes synchronous resection of two ends of a DSB. Finally, BIR is also suppressed when Sir2 silences a normally heterochromatic repair template. All of these proteins are particularly important for limiting BIR when recombination occurs between short repetitive sequences, emphasizing the significance of these mechanisms for species carrying many repetitive elements such as humans.
同源重组过程中的 DNA 合成具有高度突变性，并且容易发生模板转换。两端 DNA 双链断裂（DSB）通常通过短片段 DNA 合成的基因转换修复，从而将突变负荷限制在 DSB 附近。单端 DSB 通过断裂诱导复制（BIR）修复，涉及长达数百个千碱基的广泛和突变性 DNA 合成。目前尚不清楚如何在两端 DSB 处抑制突变性 BIR。在这里，我们证明了通过协调 DSB 两端使用的蛋白质来抑制 BIR：（i）促进第二个末端捕获的单链 DNA 退火蛋白 Rad52 和 Rad59，（ii）D 环解旋酶 Mph1，以及（iii）促进 DSB 两个末端同步切除的 Mre11-Rad50-Xrs2 复合物。最后，当 Sir2 沉默通常异染色质修复模板时，BIR 也受到抑制。所有这些蛋白质对于限制短重复序列之间发生重组时的 BIR 都特别重要，这强调了这些机制对于携带许多重复元件（如人类）的物种的重要性。
