Whitby M C, Lloyd R G
Department of Genetics, University of Nottingham, Queens Medical Centre, UK.
EMBO J. 1995 Jul 17;14(14):3302-10. doi: 10.1002/j.1460-2075.1995.tb07337.x.
RecG protein is required for normal levels of recombination and DNA repair in Escherichia coli. This 76 kDa polypeptide is a junction-specific DNA helicase that acts post-synaptically to drive branch migration of Holliday junction intermediates made by RecA during the strand exchange stage of recombination. To gain further insight into the role of RecG, we studied its activity on three-strand intermediates formed by RecA between circular single-stranded and linear duplex DNAs. Once RecA is removed, RecG drives branch migration of these intermediates by a junction-targeted activity that depends on hydrolysis of ATP. RuvAB has a similar activity. However, when RecG is added to a RecA strand exchange reaction it severely reduces the accumulation of joint molecule intermediates by driving branch migration of junctions in the reverse direction to that catalysed by RecA strand exchange. In comparison, RuvAB has little effect on the reaction. We discuss how reverse branch migration by RecG, which acts counter of the 5'-->3' polarity of RecA binding and strand exchange, could serve to promote or abort the early stages of recombination, depending on the orientation of the single DNA strand initiating the exchange relative to the adjacent duplex region.
RecG蛋白是大肠杆菌正常水平的重组和DNA修复所必需的。这种76 kDa的多肽是一种连接特异性DNA解旋酶，它在突触后起作用，驱动RecA在重组链交换阶段形成的霍利迪连接中间体的分支迁移。为了进一步深入了解RecG的作用，我们研究了它对RecA在环状单链和线性双链DNA之间形成的三链中间体的活性。一旦去除RecA，RecG通过一种依赖于ATP水解的连接靶向活性驱动这些中间体的分支迁移。RuvAB具有类似的活性。然而，当将RecG添加到RecA链交换反应中时，它会通过驱动连接以与RecA链交换催化的方向相反的方向进行分支迁移，从而严重减少联合分子中间体的积累。相比之下，RuvAB对该反应影响很小。我们讨论了RecG的反向分支迁移如何与RecA结合和链交换的5'→3'极性相反地起作用，这取决于启动交换的单链DNA相对于相邻双链区域的方向，从而促进或中止重组的早期阶段。
