Grenon M, Gilbert C, Lowndes N F
ICRF Clare Hall Laboratories, CDC Laboratory, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3LD, UK.
Nat Cell Biol. 2001 Sep;3(9):844-7. doi: 10.1038/ncb0901-844.
Studies of human Nijmegen breakage syndrome (NBS) cells have led to the proposal that the Mre11/Rad50/ NBS1 complex, which is involved in the repair of DNA double-strand breaks (DSBs), might also function in activating the DNA damage checkpoint pathways after DSBs occur. We have studied the role of the homologous budding yeast complex, Mre11/Rad50/Xrs2, in checkpoint activation in response to DSB-inducing agents. Here we show that this complex is required for phosphorylation and activation of the Rad53 and Chk1 checkpoint kinases specifically in response to DSBs. Consistent with defective Rad53 activation, we observed defective cell-cycle delays after induction of DSBs in the absence of Mre11. Furthermore, after gamma-irradiation phosphorylation of Rad9, which is an early event in checkpoint activation, is also dependent on Mre11. All three components of the Mre11/Rad50/Xrs2 complex are required for activation of Rad53, however, the Ku80, Rad51 or Rad52 proteins, which are also involved in DSB repair, are not. Thus, the integrity of the Mre11/Rad50/Xrs2 complex is specifically required for checkpoint activation after the formation of DSBs.
对人类尼美根断裂综合征（NBS）细胞的研究表明，参与DNA双链断裂（DSB）修复的Mre11/Rad50/NBS1复合物，可能在DSB发生后激活DNA损伤检查点途径中也发挥作用。我们研究了同源的芽殖酵母复合物Mre11/Rad50/Xrs2在响应DSB诱导剂时检查点激活中的作用。在此我们表明，该复合物是Rad53和Chk1检查点激酶磷酸化和激活所必需的，特别是在响应DSB时。与Rad53激活缺陷一致，我们观察到在缺乏Mre11的情况下诱导DSB后细胞周期延迟存在缺陷。此外，γ射线照射后，作为检查点激活早期事件的Rad9磷酸化也依赖于Mre11。Mre11/Rad50/Xrs2复合物的所有三个组分都是Rad53激活所必需的，然而，也参与DSB修复的Ku80、Rad51或Rad52蛋白则不是。因此，Mre11/Rad50/Xrs2复合物的完整性是DSB形成后检查点激活所特需的。
