Zhou Qingwen, Holloman William K
Department of Microbiology and Immunology, Weill Cornell Medical College , New York, New York 10065, United States.
Biochemistry. 2017 Jul 5;56(26):3318-3327. doi: 10.1021/acs.biochem.7b00184. Epub 2017 Jun 26.
Brh2, the BRCA2 ortholog in the fungus Ustilago maydis, mediates delivery of Rad51 to DNA during the course of homology-directed DNA repair. Rad51 interacts with Brh2 through the highly conserved BRC element and through a second region termed CRE located at the extreme carboxy terminus. Dss1, a small intrinsically unstructured protein that interacts with Brh2, is crucial for its activity in DNA repair, but the mechanism of this regulation is uncertain. In previous studies, we found that interaction of Brh2 with DNA was strongly modulated by association with Dss1. Here we report that CRE influences interaction of Dss1 with Brh2 and that Dss1 status markedly alters interaction of Brh2 with Rad51. While it appears that a single Rad51 protomer associates with Brh2 in complex with Dss1, loss of Dss1 is accompanied by a large increase in the number of Rad51 protomers that can associate with Brh2. Concomitant with this buildup of Rad51, Brh2 loses its ability to bind DNA. These observations suggest a feedback circuit in which release of Dss1 from Brh2 as it binds DNA triggers nucleation of a short Rad51 oligomer on Brh2, which in turn promotes dissociation of Brh2 from the DNA.
Brh2是真菌玉米黑粉菌中BRCA2的直系同源物，在同源定向DNA修复过程中介导Rad51与DNA的结合。Rad51通过高度保守的BRC元件以及位于极端羧基末端的另一个称为CRE的区域与Brh2相互作用。Dss1是一种与Brh2相互作用的小的内在无序蛋白，对其在DNA修复中的活性至关重要，但其调节机制尚不确定。在先前的研究中，我们发现Brh2与DNA的相互作用受到与Dss1结合的强烈调节。在此我们报告，CRE影响Dss1与Brh2的相互作用，并且Dss1的状态显著改变Brh2与Rad51的相互作用。虽然似乎单个Rad51原聚体在与Dss1形成的复合物中与Brh2结合，但Dss1的缺失伴随着可与Brh2结合的Rad51原聚体数量的大幅增加。伴随着Rad51的这种积累，Brh2失去了与DNA结合的能力。这些观察结果表明存在一种反馈回路，其中当Brh2结合DNA时Dss1从Brh2上释放，触发了Brh2上短Rad51寡聚体的成核，这反过来又促进了Brh2与DNA的解离。
