Rad51 paralog complex Rad55–Rad57 acts as a molecular chaperone during homologous recombination. Roy et al.

We investigated the role of Rad51 paralog complex Rad55–Rad57 in homologous recombination. We visualized Rad55–Rad57 dynamics at the single–molecule level, in real–time using total internal reflection fluorescence microscopy (TIRFM). Our data shows Rad55–Rad57 binds Rad51–ssDNA only transiently during early stages of Rad51 filament assembly, and strongly stimulates the rate of Rad51–ssDNA filament formation. Release of the paralog complex from the Rad51–ssDNA filament is dependent upon ATP hydrolysis by Rad55–Rad57. We also show that Rad55–Rad57 does not physically block translocation of the anti-recombinase Srs2, but rather counteracts it by promoting rapid Rad51 re-assembly.本研究探究了Rad51旁系同源复合体Rad55–Rad57在同源重组（homologous recombination）中的作用。本研究利用全内反射荧光显微镜（total internal reflection fluorescence microscopy, TIRFM），在单分子水平上对Rad55–Rad57的动态变化进行了实时观测。实验数据表明，Rad55–Rad57仅在Rad51丝状体组装的早期阶段，短暂结合Rad51-单链DNA（single-stranded DNA, ssDNA）复合物，并可显著促进Rad51-ssDNA丝状体的形成速率。该旁系同源复合体从Rad51-ssDNA丝状体上的解离过程，依赖于Rad55–Rad57介导的ATP水解。本研究同时证实，Rad55–Rad57并不会通过物理阻断抗重组酶（anti-recombinase）Srs2的转位来发挥功能，而是通过促进Rad51的快速重新组装来抵消Srs2的抗重组活性。