Divisions of Medicine and Biomedical and Life Sciences, School of Health and Medicine, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK.
Nucleic Acids Res. 2010 Jan;38(2):441-54. doi: 10.1093/nar/gkp905. Epub 2009 Nov 5.
The repair of DNA double-strand breaks (DSBs) is essential to maintain genomic integrity. In higher eukaryotes, DNA DSBs are predominantly repaired by non-homologous end joining (NHEJ), but DNA ends can also be joined by an alternative error-prone mechanism termed microhomology-mediated end joining (MMEJ). In MMEJ, the repair of DNA breaks is mediated by annealing at regions of microhomology and is always associated with deletions at the break site. In budding yeast, the Mre11/Rad5/Xrs2 complex has been demonstrated to play a role in both classical NHEJ and MMEJ, but the involvement of the analogous MRE11/RAD50/NBS1 (MRN) complex in end joining in higher eukaryotes is less certain. Here we demonstrate that in Xenopus laevis egg extracts, the MRN complex is not required for classical DNA-PK-dependent NHEJ. However, the XMRN complex is necessary for resection-based end joining of mismatched DNA ends. This XMRN-dependent end joining process is independent of the core NHEJ components Ku70 and DNA-PK, occurs with delayed kinetics relative to classical NHEJ and brings about repair at sites of microhomology. These data indicate a role for the X. laevis MRN complex in MMEJ.
DNA 双链断裂 (DSBs) 的修复对于维持基因组完整性至关重要。在高等真核生物中，DNA DSBs 主要通过非同源末端连接 (NHEJ) 进行修复，但 DNA 末端也可以通过另一种易错的机制——微同源介导的末端连接 (MMEJ) 进行连接。在 MMEJ 中，DNA 断裂的修复是通过微同源区域的退火介导的，并且总是与断裂部位的缺失相关。在 budding 酵母中，已经证明 Mre11/Rad5/Xrs2 复合物在经典 NHEJ 和 MMEJ 中都发挥作用，但类似的 MRE11/RAD50/NBS1 (MRN) 复合物在高等真核生物中参与末端连接的情况则不太确定。在这里，我们证明在非洲爪蟾卵提取物中，MRN 复合物不是经典的 DNA-PK 依赖性 NHEJ 所必需的。然而，XMRN 复合物对于错配 DNA 末端的基于切除的末端连接是必需的。这种依赖 XMRN 的末端连接过程不依赖于核心 NHEJ 组件 Ku70 和 DNA-PK，与经典 NHEJ 相比具有延迟的动力学，并且在微同源区域进行修复。这些数据表明，非洲爪蟾的 MRN 复合物在 MMEJ 中发挥作用。
