Wencker Freya D R, Marincola Gabriella, Schoenfelder Sonja M K, Maaß Sandra, Becher Dörte, Ziebuhr Wilma
Institute of Molecular Infection Biology, University of Würzburg, Würzburg 97080, Germany.
Institute of Microbiology, University of Greifswald, Greifswald 17489, Germany.
Nucleic Acids Res. 2021 Feb 26;49(4):2192-2212. doi: 10.1093/nar/gkaa1277.
In Staphylococcus aureus, de novo methionine biosynthesis is regulated by a unique hierarchical pathway involving stringent-response controlled CodY repression in combination with a T-box riboswitch and RNA decay. The T-box riboswitch residing in the 5' untranslated region (met leader RNA) of the S. aureus metICFE-mdh operon controls downstream gene transcription upon interaction with uncharged methionyl-tRNA. met leader and metICFE-mdh (m)RNAs undergo RNase-mediated degradation in a process whose molecular details are poorly understood. Here we determined the secondary structure of the met leader RNA and found the element to harbor, beyond other conserved T-box riboswitch structural features, a terminator helix which is target for RNase III endoribonucleolytic cleavage. As the terminator is a thermodynamically highly stable structure, it also forms posttranscriptionally in met leader/ metICFE-mdh read-through transcripts. Cleavage by RNase III releases the met leader from metICFE-mdh mRNA and initiates RNase J-mediated degradation of the mRNA from the 5'-end. Of note, metICFE-mdh mRNA stability varies over the length of the transcript with a longer lifespan towards the 3'-end. The obtained data suggest that coordinated RNA decay represents another checkpoint in a complex regulatory network that adjusts costly methionine biosynthesis to current metabolic requirements.
在金黄色葡萄球菌中，甲硫氨酸的从头生物合成由一条独特的分级途径调控，该途径涉及严格反应控制的CodY抑制，以及一个T-box核糖开关和RNA降解。位于金黄色葡萄球菌metICFE-mdh操纵子5'非翻译区（met前导RNA）的T-box核糖开关在与未负载的甲硫氨酰-tRNA相互作用时控制下游基因转录。met前导RNA和metICFE-mdh（m）RNA在一个分子细节尚不清楚的过程中经历核糖核酸酶介导的降解。在这里，我们确定了met前导RNA的二级结构，发现该元件除了具有其他保守的T-box核糖开关结构特征外，还含有一个终止螺旋，它是核糖核酸酶III内切核糖核酸酶切割的靶点。由于终止子是一种热力学上高度稳定的结构，它也在转录后在met前导/metICFE-mdh通读转录本中形成。核糖核酸酶III的切割从metICFE-mdh mRNA上释放出met前导RNA，并启动核糖核酸酶J介导的从5'端开始的mRNA降解。值得注意的是，metICFE-mdh mRNA的稳定性在转录本的长度上有所不同，3'端的寿命更长。获得的数据表明，协调的RNA降解代表了复杂调控网络中的另一个检查点，该网络将昂贵的甲硫氨酸生物合成调整到当前的代谢需求。
