Cross-talk between DNA repaif and recombination : two kinds of mechanisms that are mediated by DNA end-joining

我们利用新开发的检测系统分析了大肠杆菌、芽殖酵母、裂变酵母和小鼠的非合法重组机制及其与DNA修复机制的关系。通过对具有超重组表型的E.coil DNA螺旋酶突变体的分析，我们发现DNA螺旋酶的几个α-螺旋结构在非法重组中起重要作用。E.coil DNA结合蛋白HU具有抑制DNA回转介导的非法重组的活性，从而对重组起到调控作用。我们还发现DNA解旋酶、核酸外切酶VIII （RecE）、RecT和DNA连接酶参与了大肠杆菌DNA损伤诱导的非法重组。此外，许多DNA修复酶UvrA、UvrB、MutM、Tag、AIkA、ExoI、H-NS和StpA在抑制DNA损伤诱导的非法重组中发挥重要作用。在酿酒酵母中发现一种DNA拓扑异构体II抑制剂诱导非法重组，提示DNA拓扑异构体II通过DNA末端连接促进DNA双链断裂，进而促进非法重组。另一方面，研究表明Sgsl蛋白抑制自发的非法重组。人类BLM和WRN蛋白也抑制了出芽酵母中的非法重组。此外，我们发现出芽酵母Sccl和裂变酵母Dhpl蛋白参与DNA修复和染色体分离，出芽酵母Whip和裂变酵母Mogi和Hskl激酶分别与Sgs 1和Sec 1相互作用。基于这些结果，我们提出了E.coil和酵母的几种不正当重组模型。

We analysed mechanisms of illegitimate recombination and its relationship with mechanisms of DNA repair, using newly developed assay systems for illegitimate recombination in Escherichia coli, budding yeast, fission yeast and mouse. Based on the analyses of E.coil DNA gyrase mutants that confer a hyper-recombination phenotype, we showed that several α-helix structures of DNA gyrase plays an important role in illegitimate recombination. It is also shown that E.coil DNA binding protein HU has an activity that suppress DNA gyrasemediated illegitimate recombination, thus playing a role in regulation of the recombination. We have also found that DnaB helicase, exonuclease VIII (RecE), RecT, and DNA ligase are involved in DNA damage-induced illegitimate recombmation in E. coli. Furthermore, many DNA repair enzymes UvrA, UvrB, MutM, Tag, AIkA, ExoI, H-NS, and StpA play important roles for suppression of DNA damage-induced illegitimate recombination. In Saccharomyces cerevisiae, it was found that a DNA topoisomemse II inhibitor induces illegitimate recombination, suggesting that DNA topoisomemse II promotes DNA double-strand bieak and then illegitimate recombination throgh DNA end-joining. It is, on the other hand, shown that Sgsl protein suppresses spontaneous illegitimate recombination. Human BLM and WRN proteins also suppressed illegitimate recombination in budding yeast. In addition, we showed that budding yeast Sccl and fission yeast Dhpl proteins are involved in DNA repair and chromosome segregation and that budding yeast Whip and fission yeast Mogi and Hskl kinase interact with Sgs 1 and Sec 1, respectively. Based on these results, we proposed several models for illegitimate recombination in E.coil and yeast.