Mg 2+ regulates transcription of mgtA in Salmonella Typhimurium via translation of proline codons during synthesis of the MgtL peptide

Significance Mg 2+ is an important signal for the regulation of virulence and thermotolerance in Salmonella enterica . Transcription of the mgtA gene, which encodes a transporter for Mg 2+ , is highly induced by Mg 2+ limitation. The 5′ leader of the mgtA mRNA encodes mgtL , a 17-codon, proline-rich open reading frame, whose translation controls the transcription of mgtA : efficient translation of mgtL results in termination of transcription upstream of the mgtA protein-coding region, whereas slow or incomplete translation of mgtL antagonizes this termination. We show that the proline codons in mgtL present an impediment to translation at low but not high Mg 2+ concentrations, and thereby, we provide a model for how Mg 2+ is coupled to the regulation of mgtA transcription.