Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA.
Cell Rep. 2013 Jun 27;3(6):2033-45. doi: 10.1016/j.celrep.2013.05.026. Epub 2013 Jun 13.
Single-ended double-strand breaks (DSBs) are a common form of spontaneous DNA break, generated when the replisome encounters a discontinuity in the DNA template. Given their prevalence, understanding the mechanisms governing the fate(s) of single-ended DSBs is important. We describe the influence of the Ku heterodimer and Mre11 nuclease activity on processing of single-ended DSBs. Separation-of-function alleles of yku70 were derived that phenocopy Ku deficiency with respect to single-ended DSBs but remain proficient for NHEJ. The Ku mutants fail to regulate Exo1 activity, and bypass the requirement for Mre11 nuclease activity in the repair of camptothecin-induced single-ended DSBs. Ku mutants exhibited reduced affinity for DNA ends, manifest as both reduced end engagement and enhanced probability of diffusing inward on linear DNA. This study reveals an interplay between Ku and Mre11 in the metabolism of single-ended DSBs that is distinct from repair pathway choice at double-ended DSBs.
单链末端双链断裂（DSBs）是一种常见的自发 DNA 断裂形式，当复制体遇到 DNA 模板中的不连续性时就会产生。鉴于它们的普遍性，了解控制单链末端 DSBs 命运的机制非常重要。我们描述了 Ku 异二聚体和 Mre11 核酸酶活性对单链末端 DSBs 处理的影响。衍生出的 yku70 分离功能等位基因在单链末端 DSBs 方面表现出类似于 Ku 缺陷的表型，但仍能有效进行非同源末端连接（NHEJ）。Ku 突变体不能调节 Exo1 活性，并且在修复喜树碱诱导的单链末端 DSBs 时绕过了对 Mre11 核酸酶活性的要求。Ku 突变体对 DNA 末端的亲和力降低，表现在线性 DNA 上的末端结合减少和向内扩散的概率增加。这项研究揭示了 Ku 和 Mre11 在单链末端 DSBs 代谢中的相互作用，与双链末端 DSBs 修复途径选择不同。
