Department of Genetics & Development, Columbia University, New York, NY 10032, USA.
Department of Biochemistry & Molecular Biophysics, Columbia University, New York, NY 10032, USA; Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, X5000 HUA, Argentina.
Cell Rep. 2017 Dec 12;21(11):3166-3177. doi: 10.1016/j.celrep.2017.11.047.
Srs2 is a superfamily 1 (SF1) helicase and antirecombinase that is required for genome integrity. However, the mechanisms that regulate Srs2 remain poorly understood. Here, we visualize Srs2 as it acts upon single-stranded DNA (ssDNA) bound by the Rad51 recombinase. We demonstrate that Srs2 is a processive translocase capable of stripping thousands of Rad51 molecules from ssDNA at a rate of ∼50 monomers/s. We show that Srs2 is recruited to RPA clusters embedded between Rad51 filaments and that multimeric arrays of Srs2 assemble during translocation on ssDNA through a mechanism involving iterative Srs2 loading events at sites cleared of Rad51. We also demonstrate that Srs2 acts on heteroduplex DNA joints through two alternative pathways, both of which result in rapid disruption of the heteroduplex intermediate. On the basis of these findings, we present a model describing the recruitment and regulation of Srs2 as it acts upon homologous recombination intermediates.
Srs2 是一种超家族 1（SF1）解旋酶和抗重组酶，对于基因组完整性至关重要。然而，调节 Srs2 的机制仍知之甚少。在这里，我们观察到 Srs2 作用于 Rad51 重组酶结合的单链 DNA（ssDNA）。我们证明 Srs2 是一种具有行进性的易位酶，能够以约 50 个单体/s 的速度从 ssDNA 上剥离数千个 Rad51 分子。我们表明，Srs2 被招募到嵌入 Rad51 纤维之间的 RPA 簇中，并且在 ssDNA 上易位时，Srs2 的多聚体阵列通过涉及在 Rad51 清除位点处的迭代 Srs2 加载事件的机制组装。我们还证明 Srs2 通过两种替代途径作用于异源双链 DNA 接头，这两种途径都导致异源双链中间体的快速破坏。基于这些发现，我们提出了一个模型，描述了 Srs2 作为同源重组中间体的募集和调节。
