TheSalmonella entericaSerovar TyphiltrRGene Encodes Two Proteins Whose Transcriptional Expression Is Upregulated by Alkaline pH and Repressed at Their Promoters and Coding Regions by H-NS and Lrp

Abstract

ABSTRACTLtrR is a LysR-type regulator involved in the positive expression ofompRto promoteompCandompFexpression. This regulatory network is fundamental for the control of bacterial transformation and resistance to the bile salt sodium deoxycholate inSalmonella entericaserovar Typhi. In this work, the transcriptional regulation ofltrRwas characterized, revealing that the use of alternative promoters results in two transcripts. The larger one, theltrR2mRNA, 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 shorterltrR1transcript, 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 bothltrRunits. Translational fusions and Western blot experiments demonstrated thatltrR2andltrR1mRNAs 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.IMPORTANCEThe 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 theltrRgene. 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.