Seigneur M, Ehrlich S D, Michel B
Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas Cedex, France.
Mol Microbiol. 2000 Nov;38(3):565-74. doi: 10.1046/j.1365-2958.2000.02152.x.
Replication fork arrest can cause DNA double-strand breaks (DSBs). These DSBs are caused by the action of the Holliday junction resolvase RuvABC, indicating that they are made by resolution of Holliday junctions formed at blocked forks. In this work, we study the homologous recombination functions required for RuvABC-mediated breakage in cells deficient for the accessory replicative helicase Rep or deficient for the main Escherichia coli replicative helicase DnaB. We show that, in the rep mutant, RuvABC-mediated breakage occurs in the absence of the homologous recombination protein RecA. In contrast, in dnaBts mutants, most of the RuvABC-mediated breakage depends on the presence of RecA, which suggests that RecA participates in the formation of Holliday junctions at forks blocked by the inactivation of DnaB. This action of RecA does not involve the induction of the SOS response and does not require any of the recombination proteins essential for the presynaptic step of homologous recombination, RecBCD, RecF or RecO. Consequently, our observations suggest a new function for RecA at blocked replication forks, and we propose that RecA acts by promoting homologous recombination without the assistance of known presynaptic proteins.
复制叉停滞可导致DNA双链断裂（DSB）。这些DSB是由霍利迪连接体解离酶RuvABC的作用引起的，这表明它们是由在受阻复制叉处形成的霍利迪连接体的解离产生的。在这项工作中，我们研究了在辅助复制解旋酶Rep缺陷或主要大肠杆菌复制解旋酶DnaB缺陷的细胞中，RuvABC介导的断裂所需的同源重组功能。我们发现，在rep突变体中，RuvABC介导的断裂在没有同源重组蛋白RecA的情况下发生。相反，在dnaBts突变体中，大多数RuvABC介导的断裂依赖于RecA的存在，这表明RecA参与了在因DnaB失活而受阻的复制叉处霍利迪连接体的形成。RecA的这种作用不涉及SOS反应的诱导，也不需要同源重组突触前步骤所必需的任何重组蛋白RecBCD、RecF或RecO。因此，我们的观察结果表明RecA在受阻复制叉处具有新功能，并且我们提出RecA通过在没有已知突触前蛋白协助的情况下促进同源重组来发挥作用。
