title: Tandem attenuators control expression of the Salmonella mgtCBR virulence operon.
abstract: The mgtCBR operon from Salmonella enterica serovar Typhimurium specifies the virulence protein MgtC, the Mg(2+)  transporter MgtB and the regulatory peptide MgtR. The mgtCBR transcript includes a long leader region harbouring two short open reading frames (ORFs). Translation of these ORFs is anticipated to impact the formation of particular stem-loop structures and control transcription of the coding region by an attenuation-like mechanism. We previously reported that ORF mgtM enables Salmonella to promote transcription of the mgtC and mgtB coding regions when experiencing a rise in cytoplasmic ATP levels. We now show that the proline codon-rich ORF mgtP mediates an increase in transcription of the mgtC and mgtB coding regions under conditions predicted to decrease the levels of proline-charged tRNA(Pro) . The high ATP and low proline signals act independently in an additive form. Replacing conserved mgtP proline codons with codons specifying other amino acids abolished the response to proline limitation but had no effect on the response to ATP. Substitution of conserved adenine nucleotides in mgtM abolished the response to ATP but had no effect in the response to proline limitation. This provides a singular example of a leader mRNA with tandem attenuators responding to different signals.
authors.affiliation: Howard Hughes Medical Institute, Yale School of Medicine, Department of Microbial Pathogenesis, Boyer Center for Molecular Medicine, New Haven, CT 06536-0812, USA.
authors.forename: Eun-Jin
authors.initials: EJ
authors.lastname: Lee
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Groisman
mesh_terms: D020121:5' Untranslated Regions; D000251:Adenosine Triphosphatases / Q000096:biosynthesis* / Q000235:genetics; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D027682:Cation Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D016366:Open Reading Frames; D009876:Operon; D014176:Protein Biosynthesis; D012361:RNA, Transfer, Pro / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics*; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D014774:Virulence; D037521:Virulence Factors / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D012361:RNA, Transfer, Pro; D014157:Transcription Factors; D037521:Virulence Factors; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C083836:MgtB protein, Salmonella typhimurium; C093586:MgtC protein, Salmonella typhimurium