Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
Department of Biochemistry and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
Mol Cell. 2021 Mar 4;81(5):1043-1057.e8. doi: 10.1016/j.molcel.2020.12.019. Epub 2021 Jan 8.
Homologous recombination (HR) is essential for maintenance of genome integrity. Rad51 paralogs fulfill a conserved but undefined role in HR, and their mutations are associated with increased cancer risk in humans. Here, we use single-molecule imaging to reveal that the Saccharomyces cerevisiae Rad51 paralog complex Rad55-Rad57 promotes assembly of Rad51 recombinase filament through transient interactions, providing evidence that it acts like a classical molecular chaperone. Srs2 is an ATP-dependent anti-recombinase that downregulates HR by actively dismantling Rad51 filaments. Contrary to the current model, we find that Rad55-Rad57 does not physically block the movement of Srs2. Instead, Rad55-Rad57 promotes rapid re-assembly of Rad51 filaments after their disruption by Srs2. Our findings support a model in which Rad51 is in flux between free and single-stranded DNA (ssDNA)-bound states, the rate of which is controlled dynamically though the opposing actions of Rad55-Rad57 and Srs2.
同源重组(HR)对于维持基因组完整性至关重要。Rad51 同源物在 HR 中发挥着保守但未定义的作用,其突变与人类癌症风险增加有关。在这里,我们使用单分子成像技术揭示了酿酒酵母 Rad51 同源物复合物 Rad55-Rad57 通过瞬时相互作用促进 Rad51 重组酶丝的组装,这为其作为经典分子伴侣的作用提供了证据。Srs2 是一种依赖 ATP 的抗重组酶,通过主动拆解 Rad51 丝来下调 HR。与当前的模型相反,我们发现 Rad55-Rad57 并没有物理上阻止 Srs2 的运动。相反,Rad55-Rad57 促进了 Rad51 丝在被 Srs2 破坏后的快速重新组装。我们的发现支持了一种模型,即 Rad51 在游离和单链 DNA(ssDNA)结合状态之间处于流动状态,其速率通过 Rad55-Rad57 和 Srs2 的相反作用动态控制。