Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia.
DNA Repair (Amst). 2012 Apr 1;11(4):419-30. doi: 10.1016/j.dnarep.2012.01.011. Epub 2012 Feb 17.
In recBCD sbcB sbcC(D) mutants of Escherichia coli homologous recombination proceeds via RecF pathway, which is thought to require RecQ, UvrD and HelD helicases at its initial stage. It was previously suggested that depletion of all three helicases totally abolishes the RecF pathway. The present study (re)examines the roles of these helicases in transductional recombination, and in recombinational repair of UV-induced DNA damage in the RecF pathway. The study has employed the ΔrecBCD ΔsbcB sbcC201 and ΔrecBCD sbcB15 sbcC201 strains, carrying combinations of mutations in recQ, uvrD, and helD genes. We show that in ΔrecBCD ΔsbcB sbcC201 strains, recombination requires exclusively the RecQ helicase. In ΔrecBCD sbcB15 sbcC201 strains, RecQ may be partially substituted by UvrD helicase. The HelD helicase is dispensable for recombination in both backgrounds. Our results also suggest that significant portion of recombination events in the RecF pathway is independent of RecQ, UvrD and HelD. These events are initiated either by RecJ nuclease alone or by RecJ nuclease associated with an unknown helicase. Inactivation of exonuclease VII by a xseA mutation further decreases the requirement for helicase activity in the RecF pathway. We suggest that elimination of nucleases acting on 3' single-strand DNA ends reduces the necessity for helicases in initiation of recombination.
在大肠杆菌的 recBCD sbcB sbcC(D) 突变体中，同源重组通过 RecF 途径进行，该途径被认为在其初始阶段需要 RecQ、UvrD 和 HelD 解旋酶。先前的研究表明，三种解旋酶的耗尽完全消除了 RecF 途径。本研究（重新）检查了这些解旋酶在转导性重组以及在 RecF 途径中修复 UV 诱导的 DNA 损伤中的作用。本研究采用了Δ recBCD Δ sbcB sbcC201 和Δ recBCD sbcB15 sbcC201 菌株，这些菌株携带 recQ、uvrD 和 helD 基因的组合突变。我们表明，在Δ recBCD Δ sbcB sbcC201 菌株中，重组仅需要 RecQ 解旋酶。在Δ recBCD sbcB15 sbcC201 菌株中，RecQ 可能部分被 UvrD 解旋酶取代。HelD 解旋酶在两种背景下对重组都是可有可无的。我们的结果还表明，RecF 途径中的大部分重组事件都不依赖于 RecQ、UvrD 和 HelD。这些事件要么由 RecJ 核酸内切酶单独启动，要么由与未知解旋酶相关的 RecJ 核酸内切酶启动。通过 xseA 突变失活外切核酸酶 VII 进一步降低了 RecF 途径中解旋酶活性的要求。我们认为，消除作用于 3'单链 DNA 末端的核酸酶减少了在重组起始中解旋酶的必要性。
