Jack K D, Means J A, Hines J V
Department of Chemistry & Biochemistry, Ohio University, 100 University Terrace, Athens, OH 45701, USA.
Biochem Biophys Res Commun. 2008 May 30;370(2):306-10. doi: 10.1016/j.bbrc.2008.03.079. Epub 2008 Mar 25.
T box bacterial genes utilize a riboswitch mechanism to regulate gene expression at the transcriptional level. Complementary base pairing of the 5'-untranslated mRNA with uncharged cognate tRNA stabilizes formation of an antiterminator element and permits complete transcription. In the absence of tRNA, a mutually exclusive RNA terminator element forms and results in transcription termination. This regulatory mechanism requires divalent metal ions at the antitermination event. The structural effects of Mg(2+) binding to antiterminator model RNA were investigated to ascertain if this requirement is due to the presence of a specific metal ion binding site in the antiterminator. Spectroscopic analysis identified the presence of a hydrated, diffuse Mg(2+) binding site. The results indicate that the mechanistic requirement for divalent metal ions is not due to Mg(2+)-induced pre-formation of a functional antiterminator receptor; rather, Mg(2+) binds in a helical region of high phylogenetic sequence conservation adjacent to the tRNA binding site.
T盒细菌基因利用核糖开关机制在转录水平上调控基因表达。5'非翻译mRNA与无电荷的同源tRNA的互补碱基配对稳定了抗终止元件的形成，并允许转录完全进行。在没有tRNA的情况下，会形成互斥的RNA终止元件并导致转录终止。这种调节机制在抗终止事件中需要二价金属离子。研究了Mg(2+)与抗终止模型RNA结合的结构效应，以确定这种需求是否是由于抗终止子中存在特定的金属离子结合位点。光谱分析确定存在一个水合的、弥散的Mg(2+)结合位点。结果表明，对二价金属离子的机制需求并非由于Mg(2+)诱导功能性抗终止子受体的预先形成；相反，Mg(2+)结合在与tRNA结合位点相邻的高系统发育序列保守性的螺旋区域中。
