Bastet Laurène, Chauvier Adrien, Singh Navjot, Lussier Antony, Lamontagne Anne-Marie, Prévost Karine, Massé Eric, Wade Joseph T, Lafontaine Daniel A
Department of Biology, Faculty of Sciences, RNA Group, Université de Sherbrooke, Sherbrooke, Quebec J1K 2R1, Canada.
Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA.
Nucleic Acids Res. 2017 Jul 7;45(12):7474-7486. doi: 10.1093/nar/gkx434.
Riboswitches are regulatory elements that control gene expression by altering RNA structure upon the binding of specific metabolites. Although Bacillus subtilis riboswitches have been shown to control premature transcription termination, less is known about regulatory mechanisms employed by Escherichia coli riboswitches, which are predicted to regulate mostly at the level of translation initiation. Here, we present experimental evidence suggesting that the majority of known E. coli riboswitches control transcription termination by using the Rho transcription factor. In the case of the thiamin pyrophosphate-dependent thiM riboswitch, we find that Rho-dependent transcription termination is triggered as a consequence of translation repression. Using in vitro and in vivo assays, we show that the Rho-mediated regulation relies on RNA target elements located at the beginning of thiM coding region. Gene reporter assays indicate that relocating Rho target elements to a different gene induces transcription termination, demonstrating that such elements are modular domains controlling Rho. Our work provides strong evidence that translationally regulating riboswitches also regulate mRNA levels through an indirect control mechanism ensuring tight control of gene expression.
核糖开关是一种调控元件，通过在特定代谢物结合后改变RNA结构来控制基因表达。尽管已证明枯草芽孢杆菌核糖开关可控制转录提前终止，但对于大肠杆菌核糖开关所采用的调控机制了解较少，据预测大肠杆菌核糖开关主要在翻译起始水平进行调控。在此，我们提供了实验证据，表明大多数已知的大肠杆菌核糖开关通过使用Rho转录因子来控制转录终止。就硫胺素焦磷酸依赖性thiM核糖开关而言，我们发现Rho依赖性转录终止是翻译抑制的结果。通过体外和体内实验，我们表明Rho介导的调控依赖于位于thiM编码区起始处的RNA靶元件。基因报告实验表明，将Rho靶元件重新定位到不同基因会诱导转录终止，这表明此类元件是控制Rho的模块化结构域。我们的工作提供了有力证据，表明翻译调控的核糖开关也通过间接控制机制调节mRNA水平，从而确保对基因表达的严格控制。
