van der Oost John, Swarts Daan C, Jore Matthijs M
Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, Netherlands.
Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, Netherlands. ; Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK.
Microb Cell. 2014 Apr 15;1(5):158-159. doi: 10.15698/mic2014.05.144.
The discovery of RNA interference (RNAi) has been a major scientific breakthrough. This RNA-guided RNA interference system plays a crucial role in a wide range of regulatory and defense mechanisms in eukaryotes. The key enzyme of the RNAi system is Argonaute (Ago), an endo-ribonuclease that uses a small RNA guide molecule to specifically target a complementary RNA transcript. Two functional classes of eukaryotic Ago have been described: catalytically active Ago that cleaves RNA targets complementary to its guide, and inactive Ago that uses its guide to bind target RNA to down-regulate translation efficiency. A recent comparative genomics study has revealed that Argonaute-like proteins are also encoded by prokaryotic genomes. Interestingly, there is a lot of variation among these prokaryotic Argonaute (pAgo) proteins with respect to domain architecture: some resemble the eukaryotic Ago (long pAgo) containing a complete or disrupted catalytic site, while others are truncated versions (short pAgo) that generally contain an incomplete catalytic site. Prokaryotic Agos with an incomplete catalytic site often co-occur with (predicted) nucleases. Based on this diversity, and on the fact that homologs of other RNAi-related protein components (such as Dicer nucleases) have never been identified in prokaryotes, it has been predicted that variations on the eukaryotic RNAi theme may occur in prokaryotes.
RNA干扰（RNAi）的发现是一项重大的科学突破。这种由RNA引导的RNA干扰系统在真核生物的广泛调控和防御机制中发挥着关键作用。RNAi系统的关键酶是Argonaute（Ago），它是一种内切核糖核酸酶，利用小RNA引导分子特异性靶向互补的RNA转录本。真核生物的Ago已被描述为两种功能类别：具有催化活性的Ago，可切割与其引导序列互补的RNA靶标；以及无活性的Ago，它利用其引导序列结合靶标RNA以下调翻译效率。最近的一项比较基因组学研究表明，原核生物基因组也编码了类似Argonaute的蛋白质。有趣的是，这些原核生物Argonaute（pAgo）蛋白在结构域结构方面存在很大差异：一些类似于真核生物的Ago（长pAgo），含有完整或破坏的催化位点，而另一些是截短版本（短pAgo），通常含有不完整的催化位点。催化位点不完整的原核生物Ago通常与（预测的）核酸酶共同出现。基于这种多样性，以及在原核生物中从未鉴定出其他RNAi相关蛋白成分（如Dicer核酸酶）的同源物这一事实，有人预测原核生物中可能会出现真核生物RNAi主题的变体。
