The Salmonella enterica Serovar Typhi Gene Encodes Two Proteins Whose Transcriptional Expression Is Upregulated by Alkaline pH and Repressed at Their Promoters and Coding Regions by H-NS and Lrp.

LtrR is a LysR-type regulator involved in the positive expression of to promote and expression. This regulatory network is fundamental for the control of bacterial transformation and resistance to the bile salt sodium deoxycholate in serovar Typhi. In this work, the transcriptional regulation of was characterized, revealing that the use of alternative promoters results in two transcripts. The larger one, the mRNA, was repressed at promoter and coding regions by H-NS, whereas Lrp repressed its expression at the coding region. In the case of the second and shorter transcript, it was repressed only at the coding region by H-NS and Lrp. Remarkably, pH 7.5 is a positive signal involved in the transcriptional expression of both units. Translational fusions and Western blot experiments demonstrated that and mRNAs encode the LtrR2 and LtrR1 proteins. This study adds new data on the complex genetic and regulatory characteristics of one of the most predominant types of transcriptional factors in bacteria, the LysR-type transcriptional regulators. The LysR-type transcriptional regulators are present in viruses, archaea, bacteria, and eukaryotic cells. Furthermore, these proteins are the most abundant transcriptional factors in bacteria. Here, we demonstrate that two LysR-type proteins are generated from the gene. These proteins are genetically induced by pH and repressed at the promoter and coding regions by the global regulators H-NS and Lrp. Thus, novel basic aspects of the complex genetic regulation of the LysR-type transcriptional regulators are described.