Characterizing riboswitch function: identification of Mg2+ binding site in T box antiterminator RNA.
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.
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Department of Chemistry & Biochemistry, Ohio University, 100 University Terrace, Athens, OH 45701, USA.
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D020121:5' Untranslated Regions / Q000737:chemistry*; D001483:Base Sequence; D002413:Cations, Divalent / Q000737:chemistry; D002942:Circular Dichroism; D003035:Cobalt / Q000737:chemistry; D017124:Conserved Sequence; D015964:Gene Expression Regulation, Bacterial; D008274:Magnesium / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D012343:RNA, Transfer / Q000737:chemistry; D013728:Terminator Regions, Genetic
D020121:5' Untranslated Regions; D002413:Cations, Divalent; C030862:cobalt ammonium complex; D003035:Cobalt; D008345:Manganese; D012343:RNA, Transfer; D008274:Magnesium