The nonhomologous DNA end joining pathway is required for repair of most double-strand breaks in the mammalian genome. Here we use a purified biochemical NHEJ system to compare the joining of free DNA with recombinant mononucleosomal and dinucleosomal substrates to investigate ligation and local DNA end resection. We find that the nucleosomal state permits ligation in a manner dependent on the presence of free DNA flanking the nucleosome core particle. Local resection at DNA ends by the Artemis:DNA-PKcs nuclease complex is completely suppressed in all mononucleosome substrates regardless of flanking DNA up to a length of 14 bp. Like mononucleosomes, dinucleosomes lacking flanking free DNA are not joined. Therefore, the nucleosomal state imposes severe constraints on NHEJ nuclease and ligase activities.

哺乳动物基因组中大多数双链断裂的修复都需要非同源 DNA 末端连接途径。在这里，我们使用纯化的生化 NHEJ 系统来比较游离 DNA 与重组单核小体和双核小体底物的连接，以研究结扎和局部 DNA 末端切除。我们发现，核小体状态允许以依赖于核小体核心颗粒两侧游离 DNA 存在的方式进行连接。Artemis 对 DNA 末端的局部切除：DNA-PKcs 核酸酶复合物在所有单核小体底物中被完全抑制，无论侧翼 DNA 的长度是否达到 14 bp。与单核小体一样，缺乏侧翼游离 DNA 的双核小体也不会连接。因此，核小体状态对 NHEJ 核酸酶和连接酶的活性施加了严格的限制。