Replication-transcription conflicts trigger extensive DNA degradation in Escherichia coli cells lacking RecBCD
Replication-transcription conflicts trigger extensive DNA degradation in Escherichia coli cells lacking RecBCD
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DOI：
10.1016/j.dnarep.2018.08.002
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发表时间：
2018-10-01
期刊：
影响因子：
3.8
通讯作者：
Rudolph, Christian J.
中科院分区：
文献类型：
--
作者：
Dimude, Juachi U.;Midgley-Smith, Sarah L.;Rudolph, Christian J.
细菌染色体复制是从单一起点（oriC）开始的。两个叉子被组装起来，并以高速和高处理能力向相反方向行进，直到它们融合并终止于与 oriC 相对的专门区域。分叉的进行常常被紧密结合的蛋白质-DNA 复合物、拓扑应变或各种 DNA 损伤所阻碍。在大肠杆菌中，RecBCD 蛋白复合物在双链 DNA (dsDNA) 末端加工中发挥着关键作用。它在修复 dsDNA 断裂和重新启动在复制-转录冲突位点停滞的分叉方面发挥着重要作用。此外，Delta recB 细胞在终止区域显示大量 DNA 降解。在这项研究中，我们表明，在高度转录的 rrn 操纵子上复制和转录的正面相遇会使叉结构暴露于 SbcCD 等核酸酶的降解中。 SbcCD 也是 Delta recB 细胞终止区域退化的主要原因。然而，额外的过程会加剧该位置的退化。 Delta reB 细胞的复制概况（其中染色体在两个不同位置线性化）突出显示，复制终止的位置可能会对观察到的降解产生一些影响。我们的数据提高了我们对 RecBCD 在复制-转录冲突位点以及染色体复制最后阶段的作用的理解。然而，他们也强调，目前的模型是不够的，无法解释缺乏 RecBCD 的细胞中的所有分子细节。
Bacterial chromosome duplication is initiated at a single origin (oriC). Two forks are assembled and proceed in opposite directions with high speed and processivity until they fuse and terminate in a specialised area opposite to oriC. Proceeding forks are often blocked by tightly-bound protein-DNA complexes, topological strain or various DNA lesions. In Escherichia coil the RecBCD protein complex is a key player in the processing of double stranded DNA (dsDNA) ends. It has important roles in the repair of dsDNA breaks and the restart of forks stalled at sites of replication-transcription conflicts. In addition, Delta recB cells show substantial amounts of DNA degradation in the termination area. In this study we show that head-on encounters of replication and transcription at a highly-transcribed rrn operon expose fork structures to degradation by nucleases such as SbcCD. SbcCD is also mostly responsible for the degradation in the termination area of Delta recB cells. However, additional processes exacerbate degradation specifically in this location. Replication profiles from Delta recB cells in which the chromosome is linearized at two different locations highlight that the location of replication termination can have some impact on the degradation observed. Our data improve our understanding of the role of RecBCD at sites of replication-transcription conflicts as well as the final stages of chromosome duplication. However, they also highlight that current models are insufficient and cannot explain all the molecular details in cells lacking RecBCD.