Department of Microbiology, Immunology, and Molecular Genetics, and the Molecular Biology Institute, University of California, and the David Geffen School of Medicine, Los Angeles, CA 90095, USA.
DNA Repair (Amst). 2011 Nov 10;10(11):1121-30. doi: 10.1016/j.dnarep.2011.08.009. Epub 2011 Sep 21.
DNA mismatch repair (MMR) systems can be classified as either MutH-dependent or MutH-independent. In bacteria, extensive studies have been conducted with the MutH-dependent MMR in Escherichia coli and its close relatives. The picture of MutH-independent MMR in other bacteria is less clear, as MMR components other than MutS and MutL have not been identified in the majority of bacteria. Bacillus anthracis is one of the MutH-less Gram(+) bacteria in the phylum of Firmicutes. We used papillation as a tool to search for B. anthracis new mutator strains and identified a spontaneous mutator that carries a minitransposon insertion in the BAS4289 locus. The mutational frequency and specificity exhibited in this mutant were comparable to that of MMR-deficient strains with knockouts of mutL or mutS. It retained a similar UV sensitivity profile as that of the wild type. BAS4289 encodes a putative DNA helicase RecD2 that shares 30% sequence identity with Deinococcus radiodurans RecD2, a well characterized superfamily 1B helicase whose homologs are widely present in Firmicutes complete genomes. We demonstrated that the N-terminal region of RecD2, a unique sequence extension used to distinguish RecD2 from RecD1, was important for B. anthracis RecD2, as mutations in the N-terminal conserved motifs affected its DNA repair function. This is the first report of a RecD2 helicase being associated with MMR. RecD2 and our recently described YycJ protein are likely to be two additional components in the B. anthracis MutH-independent MMR system.
DNA 错配修复（MMR）系统可分为 MutH 依赖型和 MutH 非依赖型。在细菌中，已经对大肠杆菌及其近亲中的 MutH 依赖型 MMR 进行了广泛的研究。在其他细菌中，MutH 非依赖型 MMR 的情况不太清楚，因为除了 MutS 和 MutL 之外，大多数细菌中尚未鉴定出其他 MMR 成分。炭疽芽孢杆菌是厚壁菌门中缺少 MutH 的革兰氏阳性细菌之一。我们使用乳头瘤形成作为工具，寻找炭疽芽孢杆菌新的突变体菌株，并鉴定出一种自发突变体，该突变体在 BAS4289 基因座上带有一个小型转座子插入。该突变体表现出的突变频率和特异性与 mutL 或 mutS 敲除的 MMR 缺陷菌株相当。它保留了与野生型相似的 UV 敏感性谱。BAS4289 编码一种假定的 DNA 解旋酶 RecD2，它与具有高度特征的超级家族 1B 解旋酶的 Deinococcus radiodurans RecD2 具有 30%的序列同一性，其同源物广泛存在于厚壁菌门完整基因组中。我们证明了 RecD2 的 N 端区域，即用于将 RecD2 与 RecD1 区分开的独特序列延伸，对炭疽芽孢杆菌 RecD2 很重要，因为 N 端保守基序的突变会影响其 DNA 修复功能。这是第一个报道 RecD2 解旋酶与 MMR 相关的报告。RecD2 和我们最近描述的 YycJ 蛋白可能是炭疽芽孢杆菌 MutH 非依赖型 MMR 系统的另外两个组成部分。
