The Rockefeller University, Howard Hughes Medical Institute, New York, New York, USA.
Nat Struct Mol Biol. 2013 Jun;20(6):748-55. doi: 10.1038/nsmb.2573. Epub 2013 May 19.
Although homologous recombination is considered an accurate form of DNA repair, genetics suggest that the Escherichia coli translesion DNA polymerase IV (Pol IV, also known as DinB) promotes error-prone recombination during stress, which allows cells to overcome adverse conditions. However, how Pol IV functions and is regulated during recombination under stress is unknown. We show that Pol IV is highly proficient in error-prone recombination and is preferentially recruited to displacement loops (D loops) at stress-induced concentrations in vitro. We also found that high-fidelity Pol II switches to exonuclease mode at D loops, which is stimulated by topological stress and reduced deoxyribonucleotide pool concentration during stationary phase. The exonuclease activity of Pol II enables it to compete with Pol IV, which probably suppresses error-prone recombination. These findings indicate that preferential D-loop extension by Pol IV facilitates error-prone recombination and explain how Pol II reduces such errors in vivo.
虽然同源重组被认为是一种精确的 DNA 修复形式，但遗传学表明，大肠杆菌跨损伤 DNA 聚合酶 IV（Pol IV，也称为 DinB）在应激条件下促进易错重组，使细胞能够克服不利条件。然而，在应激条件下，Pol IV 如何在重组过程中发挥作用和被调控尚不清楚。我们发现，Pol IV 在易错重组中具有很高的效率，并且在体外应激诱导浓度下优先招募到置换环（D 环）。我们还发现，高保真 Pol II 在 D 环处切换到外切酶模式，这一过程受到拓扑学压力和静止期脱氧核苷酸池浓度降低的刺激。Pol II 的外切酶活性使其能够与 Pol IV 竞争，这可能抑制易错重组。这些发现表明，Pol IV 优先延伸 D 环促进易错重组，并解释了 Pol II 如何在体内减少此类错误。
