Departments of Biochemistry & Molecular Biology and Oncology, Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, Cumming School of Medicine; University of Calgary, 3330 Hospital Drive N.W., Calgary AB T2N 4N1, Canada.
Departments of Biochemistry & Molecular Biology and Oncology, Robson DNA Science Centre, Arnie Charbonneau Cancer Institute, Cumming School of Medicine; University of Calgary, 3330 Hospital Drive N.W., Calgary AB T2N 4N1, Canada.
DNA Repair (Amst). 2022 Jul;115:103332. doi: 10.1016/j.dnarep.2022.103332. Epub 2022 Apr 28.
A DNA double strand break (DSB) is primarily repaired by one of two canonical pathways, non-homologous end-joining (NHEJ) and homologous recombination (HR). NHEJ requires no or minimal end processing for ligation, whereas HR requires 5' end resection followed by a search for homology. The main event that determines the mode of repair is the initiation of 5' resection because if resection starts, then NHEJ cannot occur. Nej1 is a canonical NHEJ factor that functions at the cross-roads of repair pathway choice and prior to its function in stimulating Dnl4 ligase. Nej1 competes with Dna2, inhibiting its recruitment to DSBs and thereby inhibiting resection. The highly conserved C-terminal region (CTR) of Nej1 (330-338) is important for two events that drive NHEJ as it stimulates ligation and inhibits resection, but it is dispensable for end-bridging. By combining nej1 point mutants with nuclease-dead dna2-1, we find that Nej1-F335 is essential for end-joining whereas V338 promotes NHEJ indirectly by inhibiting Dna2-mediated resection.
DNA 双链断裂 (DSB) 主要通过两种规范途径之一进行修复，非同源末端连接 (NHEJ) 和同源重组 (HR)。NHEJ 不需要或只需进行最小程度的末端处理即可连接，而 HR 需要 5'端切除，然后进行同源搜索。决定修复方式的主要事件是 5'端切除的开始，因为如果开始切除，那么 NHEJ 就不能发生。Nej1 是一种规范的 NHEJ 因子，它在修复途径选择的交叉路口处发挥作用，在其刺激 Dnl4 连接酶的功能之前发挥作用。Nej1 与 Dna2 竞争，抑制其向 DSB 的募集，从而抑制切除。Nej1 的高度保守的 C 末端区域 (CTR) (330-338) 对于两个驱动 NHEJ 的事件很重要，因为它刺激连接并抑制切除，但对于末端桥接是可有可无的。通过将 nej1 点突变与核酸酶失活的 dna2-1 结合，我们发现 Nej1-F335 对于末端连接是必不可少的，而 V338 通过抑制 Dna2 介导的切除间接促进 NHEJ。
