Baylor College of Medicine, Houston, TX, United States.
DNA Repair (Amst). 2010 Apr 4;9(4):403-13. doi: 10.1016/j.dnarep.2009.12.019. Epub 2010 Feb 4.
Maintenance of genomic stability is critical for all cells. Homologous recombination (HR) pathways promote genome stability using evolutionarily conserved proteins such as RecA, SSB, and RecQ, the Escherichia coli homologue of five human proteins at least three of which suppress genome instability and cancer. A previous report indicated that RecQ promotes the net accumulation in cells of intermolecular HR intermediates (IRIs), a net effect opposite that of the yeast and two human RecQ homologues. Here we extend those conclusions. We demonstrate that cells that lack both UvrD, an inhibitor of RecA-mediated strand exchange, and RecG, a DNA helicase implicated in IRI resolution, are inviable. We show that the uvrD recG cells die a "death-by-recombination" in which IRIs accumulate blocking chromosome segregation. First, their death requires RecA HR protein. Second, the death is accompanied by cytogenetically visible failure to segregate chromosomes. Third, FISH analyses show that the unsegregated chromosomes have completed replication, supporting the hypothesis that unresolved IRIs prevented the segregation. Fourth, we show that RecQ and induction of the SOS response are required for the accumulation of replicated, unsegregated chromosomes and death, as are RecF, RecO, and RecJ. ExoI exonuclease and MutL mismatch-repair protein are partially required. This set of genes is similar but not identical to those that promote death-by-recombination of DeltauvrD Deltaruv cells. The data support models in which RecQ promotes the net accumulation in cells of IRIs and RecG promotes resolution of IRIs that form via pathways not wholly identical to those that produce the IRIs resolved by RuvABC. This implies that RecG resolves intermediates other than or in addition to standard Holliday junctions resolved by RuvABC. The role of RecQ in net accumulation of IRIs may be shared by one or more of its human homologues.
维持基因组稳定性对于所有细胞都至关重要。同源重组（HR）途径利用进化上保守的蛋白质（如 RecA、SSB 和 RecQ）来促进基因组稳定性，大肠杆菌中至少有 5 个人类蛋白的同源物，其中至少有 3 种能够抑制基因组不稳定性和癌症。先前的报告表明，RecQ 促进细胞内分子间 HR 中间产物（IRIs）的净积累，这是一种与酵母和两种人类 RecQ 同源物相反的净效应。在这里，我们扩展了这些结论。我们证明，缺乏 RecA 介导的链交换抑制剂 UvrD 和涉及 IRI 分辨率的 DNA 解旋酶 RecG 的细胞是无法存活的。我们表明，uvrD recG 细胞死于“重组致死”，其中 IRI 积累会阻止染色体分离。首先，它们的死亡需要 RecA HR 蛋白。其次，死亡伴随着细胞遗传学上可见的染色体分离失败。第三，FISH 分析表明，未分离的染色体已经完成了复制，支持了未解决的 IRI 阻止了分离的假说。第四，我们表明，RecQ 和 SOS 反应的诱导是积累复制、未分离染色体和死亡所必需的，RecF、RecO 和 RecJ 也是必需的。外切核酸酶 ExoI 和错配修复蛋白 MutL 部分需要。这组基因与促进 DeltauvrD Deltaruv 细胞重组致死的基因相似但不完全相同。这些数据支持这样的模型，即 RecQ 促进细胞内 IRI 的净积累，而 RecG 促进通过不完全相同的途径形成的 IRI 的分辨率，这些途径与 RuvABC 解析的 IRI 不同。这意味着 RecG 解析的中间体除了或除了 RuvABC 解析的标准 Holliday 结之外还有其他中间体。RecQ 在 IRI 净积累中的作用可能被其一个或多个人类同源物共享。
