Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Mol Cell. 2016 Dec 1;64(5):940-950. doi: 10.1016/j.molcel.2016.10.017. Epub 2016 Nov 23.
To repair a DNA double-strand break (DSB) by homologous recombination (HR), the 5'-terminated strand of the DSB must be resected. The human MRE11-RAD50-NBS1 (MRN) and CtIP proteins were implicated in the initiation of DNA end resection, but the underlying mechanism remained undefined. Here, we show that CtIP is a co-factor of the MRE11 endonuclease activity within the MRN complex. This function is absolutely dependent on CtIP phosphorylation that includes the key cyclin-dependent kinase target motif at Thr-847. Unlike in yeast, where the Xrs2/NBS1 subunit is dispensable in vitro, NBS1 is absolutely required in the human system. The MRE11 endonuclease in conjunction with RAD50, NBS1, and phosphorylated CtIP preferentially cleaves 5'-terminated DNA strands near DSBs. Our results define the initial step of HR that is particularly relevant for the processing of DSBs bearing protein blocks.
为了通过同源重组 (HR) 修复 DNA 双链断裂 (DSB)，DSB 的 5'-末端链必须被切除。人类 MRE11-RAD50-NBS1 (MRN) 和 CtIP 蛋白被牵连在 DNA 末端切除的起始过程中，但潜在的机制仍未确定。在这里，我们表明 CtIP 是 MRN 复合物中 MRE11 内切酶活性的辅助因子。该功能绝对依赖于 CtIP 磷酸化，包括关键的周期蛋白依赖性激酶靶标 Thr-847 。与酵母不同，Xrs2/NBS1 亚基在体外是可有可无的，而在人类系统中 NBS1 是绝对必需的。MRE11 内切酶与 RAD50、NBS1 和磷酸化的 CtIP 一起，优先切割 DSB 附近的 5'-末端 DNA 链。我们的结果定义了 HR 的初始步骤，这对于处理带有蛋白质块的 DSB 特别相关。
