Chemical modifications and adducts at DNA double-strand break (DSB) ends must be cleaned before re-joining by non-homologous end-joining (NHEJ). MRE11 nuclease is essential for efficient removal of Topoisomerase II (TOP2)-DNA adducts from TOP2 poison-induced DSBs. However, mechanisms in MRE11 recruitment to DSB sites in G₁ phase remain poorly understood. Here, we report that TOP2-DNA adducts are expeditiously removed through UBC13-mediated polyubiquitination, which promotes DSB resection in G₂ phase. We found that this ubiquitin signaling is required for efficient recruitment of MRE11 onto DSB sites in G₁ by facilitating localization of RAP80 and BRCA1 to DSB sites and complex formation between BRCA1 and MRE11 at DSB sites. UBC13 and MRE11 are dispensable for restriction-enzyme-induced “clean” DSBs repair but responsible for over 50% and 70% of NHEJ-dependent repair of γ-ray-induced “dirty” DSBs, respectively. In conclusion, ubiquitin signaling promotes nucleolytic removal of DSB blocking adducts by MRE11 before NHEJ.

在通过非同源末端连接 (NHEJ) 重新连接之前，必须清除 DNA 双链断裂 (DSB) 末端的化学修饰和加合物。 MRE11 核酸酶对于有效去除 TOP2 毒物诱导的 DSB 中的拓扑异构酶 II (TOP2)-DNA 加合物至关重要。然而，MRE11 在 G ₁期招募至 DSB 位点的机制仍知之甚少。在此，我们报告通过 UBC13 介导的多聚泛素化迅速去除 TOP2-DNA 加合物，从而促进 G ₂期的 DSB 切除。我们发现，这种泛素信号传导是通过促进 RAP80 和 BRCA1 定位到 DSB 位点以及 BRCA1 和 MRE11 在 DSB 位点之间形成复合物，将 MRE11 有效招募到 G ₁中的 DSB 位点所必需的。 UBC13 和 MRE11 对于限制性酶诱导的“干净”DSB 修复是可有可无的，但分别负责 γ 射线诱导的“脏”DSB 的 NHEJ 依赖性修复的 50% 和 70% 以上。总之，泛素信号传导促进 MRE11 在 NHEJ 之前溶核去除 DSB 阻断加合物。