PDF(Pubmed)
Abstract：
While the molecular repertoire of the homologous recombination pathways is well studied, the search mechanism that enables recombination between distant homologous regions is poorly understood. Earlier work suggests that the recombinase RecA, an essential component for homology search, forms an elongated filament, nucleating at the break site. How this RecA structure carries out long-distance search remains unclear. Here, we follow the dynamics of RecA after induction of a single double-strand break on the Caulobacter chromosome. We find that the RecA-nucleoprotein filament, once formed, rapidly translocates in a directional manner in the cell, undergoing several pole-to-pole traversals, until homology search is complete. Concomitant with translocation, we observe dynamic variation in the length of the filament. Importantly in vivo, the RecA filament alone is incapable of such long-distance movement; both translocation and associated length variations are contingent on action of structural maintenance of chromosome (SMC)-like protein RecN, via its ATPase cycle. In summary, we have uncovered the three key elements of homology search driven by RecN: mobility of a finite segment of RecA, changes in filament length, and ability to conduct multiple pole-to-pole traversals, which together point to an optimal search strategy.
摘要：
虽然同源重组途径的分子库得到了很好的研究，能够在遥远的同源区域之间进行重组的搜索机制知之甚少。早期的工作表明重组酶RecA，同源性搜索的重要组成部分，形成细长的细丝，在断裂部位成核。这种RecA结构如何进行长距离搜索尚不清楚。这里,我们跟踪RecA在Caulobacter染色体上诱导单个双链断裂后的动力学。我们发现RecA-核蛋白丝,一旦形成，在细胞中以定向的方式快速易位，经历了几次极点到极点的穿越，直到同源性搜索完成。伴随着易位，我们观察到灯丝长度的动态变化。重要的是在体内，单独的RecA细丝不能进行这种长距离移动；易位和相关的长度变化都取决于染色体（SMC）样蛋白RecN的结构维持作用，通过它的ATP酶循环。总之,我们已经发现了RecN驱动的同源性搜索的三个关键要素：RecA有限段的移动性，灯丝长度的变化，以及进行多次极点到极点遍历的能力，它们共同指向最优搜索策略。
