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首页> 外文期刊>Molecular and Cellular Biology >Inhibition of chloroplast DNA recombination and repair by dominant negative mutants of Escherichia coli RecA.
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Inhibition of chloroplast DNA recombination and repair by dominant negative mutants of Escherichia coli RecA.

机译：大肠杆菌RecA的显性负突变体抑制叶绿体DNA重组和修复。

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The occurrence of homologous DNA recombination in chloroplasts is well documented, but little is known about the molecular mechanisms involved or their biological significance. The endosymbiotic origin of plastids and the recent finding of an Arabidopsis nuclear gene, encoding a chloroplast-localized protein homologous to Escherichia coli RecA, suggest that the plastid recombination system is related to its eubacterial counterpart. Therefore, we examined whether dominant negative mutants of the E. coli RecA protein can interfere with the activity of their putative homolog in the chloroplast of the unicellular green alga Chlamydomonas reinhardtii. Transformants expressing these mutant RecA proteins showed reduced survival rates when exposed to DNA-damaging agents, deficient repair of chloroplast DNA, and diminished plastid DNA recombination. These results strongly support the existence of a RecA-mediated recombination system in chloroplasts. We also found that the wild-type E. coli RecA protein enhances the frequency of plastid DNA recombination over 15-fold, although it has no effect on DNA repair or cell survival. Thus, chloroplast DNA recombination appears to be limited by the availability of enzymes involved in strand exchange rather than by the level of initiating DNA substrates. Our observations suggest that a primary biological role of the recombination system in plastids is in the repair of their DNA, most likely needed to cope with damage due to photooxidation and other environmental stresses. This hypothesis could explain the evolutionary conservation of DNA recombination in chloroplasts despite the predominantly uniparental inheritance of their genomes.
机译：叶绿体中同源DNA重组的发生已得到充分记录，但对涉及的分子机制或其生物学意义了解甚少。质体的内共生起源和拟南芥核基因的最新发现，该基因编码与大肠杆菌RecA同源的叶绿体定位蛋白，表明质体重组系统与其真细菌对应。因此，我们检查了大肠杆菌RecA蛋白的显性负突变体是否会干扰单细胞绿藻莱茵衣藻的叶绿体中其推定同源物的活性。表达这些突变的RecA蛋白的转化子暴露于DNA破坏剂时存活率降低，叶绿体DNA修复不足，质体DNA重组减少。这些结果有力地支持了叶绿体中RecA介导的重组系统的存在。我们还发现，野生型大肠杆菌RecA蛋白可将质体DNA重组的频率提高15倍以上，尽管它对DNA修复或细胞存活没有影响。因此，叶绿体DNA重组似乎受到链交换所涉及酶的可用性的限制，而不是受到起始DNA底物水平的限制。我们的观察结果表明，质体中重组系统的主要生物学作用是修复其DNA，这很可能是应对光氧化和其他环境压力造成的损害的必要条件。该假设可以解释尽管叶绿体的基因组主要是单亲​​遗传，但叶绿体中DNA重组的进化保守性。

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