Department of Biochemistry, New York University School of Medicine, New York, NY 10016, USA.
Cell. 2011 Aug 19;146(4):533-43. doi: 10.1016/j.cell.2011.07.034.
Frequent codirectional collisions between the replisome and RNA polymerase (RNAP) are inevitable because the rate of replication is much faster than that of transcription. Here we show that, in E. coli, the outcome of such collisions depends on the productive state of transcription elongation complexes (ECs). Codirectional collisions with backtracked (arrested) ECs lead to DNA double-strand breaks (DSBs), whereas head-on collisions do not. A mechanistic model is proposed to explain backtracking-mediated DSBs. We further show that bacteria employ various strategies to avoid replisome collisions with backtracked RNAP, the most general of which is translation that prevents RNAP backtracking. If translation is abrogated, DSBs are suppressed by elongation factors that either prevent backtracking or reactivate backtracked ECs. Finally, termination factors also contribute to genomic stability by removing arrested ECs. Our results establish RNAP backtracking as the intrinsic hazard to chromosomal integrity and implicate active ribosomes and other anti-backtracking mechanisms in genome maintenance.
复制体与 RNA 聚合酶（RNAP）频繁的同向碰撞是不可避免的，因为复制的速度比转录快得多。在这里，我们表明，在大肠杆菌中，这种碰撞的结果取决于转录延伸复合物（EC）的有活性状态。与回溯（停滞）EC 的同向碰撞会导致 DNA 双链断裂（DSBs），而正面碰撞则不会。提出了一个机械模型来解释回溯介导的 DSB。我们进一步表明，细菌采用各种策略来避免与回溯的 RNA 聚合酶发生复制体碰撞，最常见的策略是阻止 RNA 聚合酶回溯的翻译。如果翻译被阻断，通过防止回溯或重新激活回溯 EC 的延伸因子来抑制 DSB。最后，终止因子通过去除停滞的 EC 也有助于基因组的稳定性。我们的结果确立了 RNA 聚合酶回溯作为染色体完整性的内在危险，并暗示活跃的核糖体和其他反回溯机制在基因组维护中发挥作用。
