The bacterial enzyme RppH triggers messenger RNA degradation by 5' pyrophosphate removal
The bacterial enzyme RppH triggers messenger RNA degradation by 5' pyrophosphate removal
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DOI：
10.1038/nature06475
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发表时间：
2008-01-17
期刊：
影响因子：
64.8
通讯作者：
Belasco, Joel G.
中科院分区：
文献类型：
--
作者：
Deana, Atilio;Celesnik, Helena;Belasco, Joel G.
大肠杆菌中信使RNA（mRNA）降解始于核酸内切裂解的长期假设受到了最近发现的挑战，即RNA降解可以由标记转录物快速周转的先前非核酸裂解事件触发：5'末端从三磷酸到一磷酸的速率决定性转化（1）.这种修饰为核酸内切酶RNase E创造了更好的底物，当RNA 5'端被单磷酸化时，其在内部位点的切割活性大大增强（2，3）。此外，它还解释了5'末端对三磷酸化初级转录物的核酸内切切割的影响（4-）（8）。然而，在任何细菌物种中都没有鉴定出能够从RNA 5'末端去除焦磷酸的酶。在这里，我们表明，E。大肠杆菌蛋白RppH（以前称为NudH/Y gdP）是RNA焦磷酸水解酶，其通过这种5 '末端依赖性途径启动mRNA降解。在体外，RppH有效地从三磷酸化RNA的5'末端去除焦磷酸，而不管5'末端核苷酸的身份。在体内，它加速了数百种E.通过将它们的三磷酸化的5'端转化为更不稳定的单磷酸化状态，可以刺激随后的核糖核酸酶切割，从而使它们与大肠杆菌转录物结合。当5'端被茎环结构隔离时，焦磷酸水解酶的作用受到阻碍，这有助于解释5'端碱基配对对mRNA寿命的稳定影响。总之，这些发现表明RppH及其直系同源物对细菌病原体的侵袭性的影响的可能基础。有趣的是，在E.大肠杆菌不仅催化一个过程，功能上让人想起真核生物的mRNA去帽，但也承担了真核生物的去帽酶Dcp 2的进化关系。
The long- standing assumption that messenger RNA ( mRNA) degradation in Escherichia coli begins with endonucleolytic cleavage has been challenged by the recent discovery that RNA decay can be triggered by a prior non- nucleolytic event that marks transcripts for rapid turnover: the rate- determining conversion of the 5' terminus from a triphosphate to a monophosphate(1). This modification creates better substrates for the endonuclease RNase E, whose cleavage activity at internal sites is greatly enhanced when the RNA 5' end is monophosphorylated(2,3). Moreover, it suggests an explanation for the influence of 5' termini on the endonucleolytic cleavage of primary transcripts, which are triphosphorylated(4-) (8). However, no enzyme capable of removing pyrophosphate from RNA 5' ends has been identified in any bacterial species. Here we show that the E. coli protein RppH ( formerly NudH/Y gdP) is the RNA pyrophosphohydrolase that initiates mRNA decay by this 5'- end- dependent pathway. In vitro, RppH efficiently removes pyrophosphate from the 5' end of triphosphorylated RNA, irrespective of the identity of the 5'- terminal nucleotide. In vivo, it accelerates the degradation of hundreds of E. coli transcripts by converting their triphosphorylated 5' ends to a more labile mono-phosphorylated state that can stimulate subsequent ribonuclease cleavage. That the action of the pyrophosphohydrolase is impeded when the 5' end is structurally sequestered by a stem- loop helps to explain the stabilizing influence of 5'- terminal base pairing on mRNA lifetimes. Together, these findings suggest a possible basis for the effect of RppH and its orthologues on the invasiveness of bacterial pathogens. Interestingly, this master regulator of 5'- end-dependent mRNA degradation in E. coli not only catalyses a process functionally reminiscent of eukaryotic mRNA decapping but also bears an evolutionary relationship to the eukaryotic decapping enzyme Dcp2.