Kim Jong-Soo, Krasieva Tatiana B, Kurumizaka Hitoshi, Chen David J, Taylor A Malcolm R, Yokomori Kyoko
Department of Biological Chemistry, School of Medicine, University of California, Irvine, CA 92697, USA.
J Cell Biol. 2005 Aug 1;170(3):341-7. doi: 10.1083/jcb.200411083.
Damage recognition by repair/checkpoint factors is the critical first step of the DNA damage response. DNA double strand breaks (DSBs) activate checkpoint signaling and are repaired by nonhomologous end-joining (NHEJ) and homologous recombination (HR) pathways. However, in vivo kinetics of the individual factor responses and the mechanism of pathway choice are not well understood. We report cell cycle and time course analyses of checkpoint activation by ataxia-telangiectasia mutated and damage site recruitment of the repair factors in response to laser-induced DSBs. We found that MRN acts as a DNA damage marker, continuously localizing at unrepaired damage sites. Damage recognition by NHEJ factors precedes that of HR factors. HR factor recruitment is not influenced by NHEJ factor assembly and occurs throughout interphase. Damage site retention of NHEJ factors is transient, whereas HR factors persist at unrepaired lesions, revealing unique roles of the two pathways in mammalian cells.
修复/检查点因子对损伤的识别是DNA损伤反应的关键第一步。DNA双链断裂（DSB）激活检查点信号，并通过非同源末端连接（NHEJ）和同源重组（HR）途径进行修复。然而，单个因子反应的体内动力学以及途径选择机制尚不清楚。我们报告了对共济失调毛细血管扩张症突变引起的检查点激活以及修复因子在激光诱导的DSB反应中损伤位点募集的细胞周期和时间进程分析。我们发现MRN作为DNA损伤标记物，持续定位于未修复的损伤位点。NHEJ因子对损伤的识别先于HR因子。HR因子的募集不受NHEJ因子组装的影响，并且在整个间期都会发生。NHEJ因子在损伤位点的保留是短暂的，而HR因子则持续存在于未修复的损伤处，揭示了这两条途径在哺乳动物细胞中的独特作用。
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