RNase H1 is an endonuclease specific toward the RNA strand of RNA:DNA hybrids. Members of this protein family are present in most living organisms and are essential for removing RNA that base pairs with DNA. It prevents detrimental effects of RNA:DNA hybrids and is involved in several biological processes. Arabidopsis thaliana has been previously shown to contain three genes encoding RNase H1 proteins that localize to three distinct cellular compartments. We show that these genes originate from two gene duplication events. One occurred in the common ancestor of dicots and produced nuclear and organellar RNase H1 paralogs. Second duplication occurred in the common ancestor of Brassicaceae and produced mitochondrial- and plastid-localized proteins. These proteins have the canonical RNase H1 activity, which requires at least four ribonucleotides for endonucleolytic digestion. Analysis of mutants in the RNase H1 genes revealed that the nuclear RNH1A and mitochondrial RNH1B are dispensable for development under normal growth conditions. However, the presence of at least one organellar RNase H1 (RNH1B or RNH1C) is required for embryonic development. The plastid-localized RNH1C affects plastid DNA copy number and sensitivity to replicative stress. Our results present the evolutionary history of RNH1 proteins in A. thaliana, demonstrate their canonical RNase H1 activity and indicate their role in early embryonic development.

中文翻译：

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拟南芥中RNase H1样蛋白的进化史和活性。

RNase H1是对RNA：DNA杂种的RNA链具有特异性的核酸内切酶。该蛋白质家族的成员存在于大多数活生物体中，对于去除与DNA碱基配对的RNA至关重要。它防止了RNA：DNA杂种的有害作用，并涉及多个生物学过程。拟南芥以前已经显示出含有三个编码RNase H1蛋白的基因，这些基因位于三个不同的细胞区室。我们显示这些基因源自两个基因重复事件。一种发生在双子叶植物的共同祖先，并产生核和细胞核RNase H1旁系同源物。第二次重复发生在十字花科的共同祖先，并产生线粒体和质体定位的蛋白质。这些蛋白质具有规范的RNase H1活性，需要至少四个核糖核苷酸才能进行核酸内切消化。RNase H1中的突变体分析基因揭示了核RNH1A和线粒体RNH1B对于在正常生长条件下发育是必不可少的。但是，胚胎发育需要至少一种细胞器RNase H1（RNH1B或RNH1C）的存在。质体定位的RNH1C影响质体DNA的拷贝数和对复制压力的敏感性。我们的结果显示了拟南芥中RNH1蛋白的进化历史，证明了其经典的RNase H1活性并表明了它们在早期胚胎发育中的作用。