The Archaeal Exosome: Degradation and Tailing at the 3′-End of RNA
The Archaeal Exosome: Degradation and Tailing at the 3′-End of RNA
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DOI：
10.1007/978-3-319-65795-0_5
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
E. Evguenieva-Hackenberg;Susann Gauernack;G. Klug
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文献类型：
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作者：
E. Evguenieva-Hackenberg;Susann Gauernack;G. Klug
许多新生RNA加工成功能分子包括在3′端的核糖核酸切割。此外，需要核糖核酸酶来去除非功能性RNA和用于mRNA降解以调节mRNA水平以满足细胞的生理需要。在大多数酵母中，RNA在3′端的加工和降解是由一种名为外泌体的蛋白质复合物完成的。古细菌外泌体从3′-端磷酸化降解RNA，释放核苷5′-二磷酸（NDP）。在逆反应中，它使用NDP在RNA的3′端合成杂聚的富含腺嘌呤的尾部，专门用于降解。外泌体由六聚体环结构和多聚体RNA结合帽组成，所述六聚体环结构由古细菌蛋白aRrp 41和aRrp 42组成，所述多聚体RNA结合帽含有三种不同的蛋白质（aRrp 4、aCsl 4和aDnaG），具有总共四种不同的RNA结合结构域（S1、KH、Zn带和aDnaG的N末端结构域）。六聚体环和可变aRrp 4-aCsl 4-异源三聚体形成古细菌外泌体的九亚基核心，该结构在细菌多核苷酸磷酸化酶（PNIPs）和真核外泌体中进化保留。然而，虽然在大多数真核外泌体中，九亚基核心是催化失活的，但细菌外泌体和古细菌外泌体在其六聚体环的通道中均含有三个磷酸解位点，并作为外核糖核酸酶和RNA加尾酶发挥作用。aDnaG是古细菌外泌体的古细菌特异性亚基，可能增加其底物多样性，有助于调节其功能并决定其亚细胞定位。
Processing of many nascent RNAs into functional molecules includes ribonucleolytic trimming at the 3′-end. Additionally, ribonucleases are needed for removal of non-functional RNAs and for mRNA degradation adjusting mRNA levels to physiological needs of the cell. In most Archaea RNA processing and degradation at the 3′-end are performed by a protein complex named exosome. The archaeal exosome degrades RNA phosphorolytically from the 3′-end releasing nucleoside 5′-diphosphates (NDPs). In a reverse reaction, it uses NDPs to synthesize heteropolymeric, adenine-rich tails at the 3′-end of RNAs dedicated to degradation. The exosome consists of a hexameric ring structure composed of the archaeal proteins aRrp41 and aRrp42, and of a multimeric RNA-binding cap containing three different proteins (aRrp4, aCsl4 and aDnaG) with totally four different RNA binding domains (S1, KH, Zn-ribbon and the N-terminal domain of aDnaG). The hexameric ring and a variable aRrp4-aCsl4-heterotrimer form the nine-subunit core of the archaeal exosome, a structure that is evolutionary preserved in the bacterial polynucleotide phosphorylase (PNPase) and in the eukaryotic exosome. However, while in most eukaryotic exosomes the nine-subunit core is catalytically inactive, both bacterial PNPase and the archaeal exosome contain three phosphorolytic sites in the channels of their hexameric rings and function as exoribonucleases and RNA tailing enzymes. aDnaG is the archaea-specific subunit of the archaeal exosome and probably increases its substrate versatility, contributes to the regulation of its functions and determines its subcellular localization.