Negative and Positive Regulation of the Non-Osmoregulated ompS1 Porin Gene in Salmonella Typhi: A Novel Regulatory Mechanism That Involves OmpR

Mol Microbiol. 1999 Apr;32(2):243-52. 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 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 / genetics*
  • Salmonella typhi / growth & development*
  • Salmonella typhi / metabolism
  • Sequence Analysis, DNA
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Transcription, Genetic
  • Water-Electrolyte Balance


  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • OmpS1 protein, Salmonella typhi
  • Porins
  • Trans-Activators
  • osmolarity response regulator proteins

Associated data

  • GENBANK/X73237