Yonetani Yasukazu, Hochegger Helfrid, Sonoda Eiichiro, Shinya Sayoko, Yoshikawa Hideki, Takeda Shunichi, Yamazoe Mistuyoshi
Department of Orthopedics, Graduate School of Medicine, Osaka University, Osaka, Japan.
Nucleic Acids Res. 2005 Aug 10;33(14):4544-52. doi: 10.1093/nar/gki766. Print 2005.
Metazoan Rad51 plays a central role in homologous DNA recombination, and its activity is controlled by a number of Rad51 cofactors. These include five Rad51 paralogs, Rad51B, Rad51C, Rad51D, XRCC2 and XRCC3. We previously hypothesized that all five paralogs participate collaboratively in repair. However, this idea was challenged by the biochemical identification of two independent complexes composed of either Rad51B/C/D/XRCC2 or Rad51C/XRCC3. To investigate if this biochemical finding is matched by genetic interactions, we made double mutants in either the same complex (rad51b/rad51d) or in both complexes (xrcc3/rad51d). In agreement with the biochemical findings the double deletion involving both complexes had an additive effect on the sensitivity to camptothecin and cisplatin. The double deletion of genes in the same complex, on the other hand, did not further increase the sensitivity to these agents. Conversely, all mutants tested displayed comparatively mild sensitivity to gamma-irradiation and attenuated gamma-irradiation-induced Rad51 foci formation. Thus, in accord with our previous conclusion, all paralogs appear to collaboratively facilitate Rad51 action. In conclusion, our detailed genetic study reveals a complex interplay between the five Rad51 paralogs and suggests that some of the Rad51 paralogs can separately operate in later step of homologous recombination.
后生动物的Rad51在同源DNA重组中起核心作用，其活性受多种Rad51辅助因子控制。这些辅助因子包括五个Rad51旁系同源物，即Rad51B、Rad51C、Rad51D、XRCC2和XRCC3。我们之前推测所有五个旁系同源物协同参与修复。然而，由Rad51B/C/D/XRCC2或Rad51C/XRCC3组成的两个独立复合物的生化鉴定对这一观点提出了挑战。为了研究这一生化发现是否与遗传相互作用相匹配，我们构建了同一复合物（rad51b/rad51d）或两个复合物（xrcc3/rad51d）中的双突变体。与生化发现一致，涉及两个复合物的双缺失对喜树碱和顺铂的敏感性具有累加效应。另一方面，同一复合物中基因的双缺失并没有进一步增加对这些药物的敏感性。相反，所有测试的突变体对γ射线显示出相对较轻的敏感性，并减弱了γ射线诱导的Rad51焦点形成。因此，与我们之前的结论一致，所有旁系同源物似乎协同促进Rad51的作用。总之，我们详细的遗传学研究揭示了五个Rad51旁系同源物之间复杂的相互作用，并表明一些Rad51旁系同源物可以在同源重组的后期步骤中单独发挥作用。
