Negative and positive regulation of the non‐osmoregulated ompS1 porin gene in Salmonella typhi : a novel regulatory mechanism that involves OmpR

• Published in: Molecular microbiology Vol. 32; no. 2; pp. 243 - 252
• Main Authors: Oropeza, Ricardo, Sampieri, Clara Luz, Puente, José Luis, Calva, Edmundo
• Format: Journal Article
• Language: English
• Published: Oxford BSL Blackwell Science Ltd 01.04.1999; Blackwell Publishing Ltd
• Subjects: Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Bacterial Proteins; Base Sequence; DNA Footprinting; Electrophoresis, Polyacrylamide Gel; Gene Deletion; Gene Expression Regulation, Bacterial; Genes, Bacterial; Genes, Reporter; Molecular Sequence Data; Porins; Promoter Regions, Genetic; Salmonella typhi; Salmonella typhi - genetics; Salmonella typhi - growth & development; Salmonella typhi - metabolism; Sequence Analysis, DNA; Trans-Activators - genetics; Trans-Activators - metabolism; Transcription, Genetic; Water-Electrolyte Balance
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.1999.01329.x

The Salmonella typhi ompS1 gene codes for an outer membrane protein of the OmpC/OmpF porin family. It is expressed at very low levels, relative to the major porins. However, deletion analysis of the 5′ regulatory region showed that the gradual removal of nucleotides −310 to −88, upstream from the P1 major transcriptional start‐point, resulted in a stepwise increase in expression, reaching levels 10‐fold above those for the ompC major porin gene. Hence, this 222 bp segment contains cis‐acting regulatory elements involved in negative control. Primer extension analysis revealed the presence of three promoters: P1 activity was OmpR dependent; P2 was expressed at a lower level in the absence of OmpR; and P3 had a minor constitutive activity. OmpR bound preferentially to box II, an 18 bp F1/C1 canonical site, the removal (−88 to −66) of which resulted in a decrease in expression thus supporting its role in positive control. Expression of ompS1 was not induced by a set of stress conditions, including a shift in osmolarity, nor was the IHF regulator involved in negative control. An ompS1 homologue was found in E. coli K‐12, which contains a nonsense codon and a shift in the reading frame, whereas Salmonella typhimurium contains an open reading frame in this region. Thus, S. typhi ompS1 provides novel features in OmpR regulation.