Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058 Basel, Switzerland; University of Basel, Faculty of Natural Sciences, 4056 Basel, Switzerland.
Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058 Basel, Switzerland.
Cell Rep. 2018 Sep 4;24(10):2614-2628.e4. doi: 10.1016/j.celrep.2018.07.102.
Multiple pathways regulate the repair of double-strand breaks (DSBs) to suppress potentially dangerous ectopic recombination. Both sequence and chromatin context are thought to influence pathway choice between non-homologous end-joining (NHEJ) and homology-driven recombination. To test the effect of repetitive sequences on break processing, we have inserted TG-rich repeats on one side of an inducible DSB at the budding yeast MAT locus on chromosome III. Five clustered Rap1 sites within a break-proximal TG repeat are sufficient to block Mre11-Rad50-Xrs2 recruitment, impair resection, and favor elongation by telomerase. The two sides of the break lose end-to-end tethering and show enhanced, uncoordinated movement. Only the TG-free side is resected and shifts to the nuclear periphery. In contrast to persistent DSBs without TG repeats that are repaired by imprecise NHEJ, nearly all survivors of repeat-proximal DSBs repair the break by a homology-driven, non-reciprocal translocation from ChrIII-R to ChrVII-L. This suppression of imprecise NHEJ at TG-repeat-flanked DSBs requires the Uls1 translocase activity.
多种途径调节双链断裂（DSB）的修复，以抑制潜在危险的异位重组。序列和染色质结构都被认为会影响非同源末端连接（NHEJ）和同源驱动重组之间的途径选择。为了测试重复序列对断裂处理的影响，我们在芽殖酵母 MAT 基因座的诱导性 DSB 的一侧插入了富含 TG 的重复序列。在靠近 TG 重复的断裂近端的 5 个簇状 Rap1 位点足以阻止 Mre11-Rad50-Xrs2 的募集，损害切除，并有利于端粒酶的延伸。断裂的两侧失去端到端的连接，并表现出增强的、不协调的运动。只有 TG 无重复的一侧被切除并转移到核周。与没有 TG 重复的持续 DSB 不同，后者通过不精确的 NHEJ 修复，几乎所有近端 TG 重复 DSB 的幸存者都通过从 ChrIII-R 到 ChrVII-L 的同源驱动、非交互易位来修复断裂。这种在 TG 重复侧翼 DSB 处抑制不精确的 NHEJ 需要 Uls1 易位酶活性。
