Iterative homology checking and non-uniform stepping during RecA-mediated strand exchange
Iterative homology checking and non-uniform stepping during RecA-mediated strand exchange
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RecA 介导的链交换过程中的迭代同源性检查和非均匀步进
DOI：
10.1016/j.bbrc.2016.08.084
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发表时间：
2016
影响因子：
3.1
通讯作者：
Ming Li
中科院分区：
文献类型：
--
作者：
Yu-Wei Zhang;Da-Guan Nong;Shuo-Xing Dou;Wei Li;Yan Yan;Xu-Guang Xi;Chun-Hua Xu;Ming Li
DNA酶介导的同源重组（HR）是两个相似或相同的DNA分子之间交换链的过程，对于维持基因组保真度和产生遗传多样性至关重要。据信，HR包括两个不同的阶段：具有严格同源性检查的初始比对，随后是逐步异源双链体扩增。然而，在异源双链扩增过程中是否以及如何进行同源性检查仍然未知。此外，每个步骤所涉及的碱基对（bp）的数量仍在争论中。通过使用单分子的方法来捕捉RecA介导的HR中具有不同程度的同源性的瞬时中间体，我们表明：（i）扩展以3 bp的倍数的步长进行，（ii）步长遵循与初始比对长度相似的宽分布，以及（iii）每个分布可以分为短尺度和长尺度部分，而不管同源性的程度如何。我们的研究结果表明了一种链交换的迭代机制，其中ssDNA-RecA细丝使用用于快速检查的短片段（6-15 bp）和用于严格序列比较的长片段（>18 bp）询问双链DNA。目前的工作提供了新的见解DNA重组的物理和结构基础。
Recombinase-mediated homologous recombination (HR) in which strands are exchanged between two similar or identical DNA molecules is essential for maintaining genome fidelity and generating genetic diversity. It is believed that HR comprises two distinct stages: an initial alignment with stringent homology checking followed by stepwise heteroduplex expansion. If and how homology checking takes place during heteroduplex expansion, however, remains unknown. In addition, the number of base pairs (bp) involved in each step is still under debate. By using single-molecule approaches to catch transient intermediates in RecA-mediated HR with different degrees of homology, we show that (i) the expansion proceeds with step sizes of multiples of 3 bp, (ii) the step sizes follow wide distributions that are similar to that of initial alignment lengths, and (iii) each distribution can be divided into a short-scale and a long-scale part irrespective of the degree of homology. Our results suggest an iterative mechanism of strand exchange in which ssDNA-RecA filament interrogates double-stranded DNA using a short tract (6–15 bp) for quick checking and a long tract (>18 bp) for stringent sequence comparison. The present work provides novel insights into the physical and structural bases of DNA recombination.