Bicarbonate-mediated transcriptional activation of divergent operons by the virulence regulatory protein, RegA, from Citrobacter rodentium

Mol Microbiol. 2008 Apr;68(2):314-27. doi: 10.1111/j.1365-2958.2008.06171.x. Epub 2008 Feb 19.


Regulation of virulence gene expression plays a central role in the pathogenesis of enteric bacteria as they encounter diverse environmental conditions in the gastrointestinal tract of their hosts. In this study, we investigated environmental regulation of two putative virulence determinants adcA and kfc by RegA, an AraC/XylS-like regulator, from Citrobacter rodentium, and identified bicarbonate as the environmental signal which induced transcription of adcA and kfc through RegA. Primer extension experiments showed that adcA and kfc were divergently transcribed from sigma(70) promoters. In vivo and in vitro experiments demonstrated that bicarbonate facilitated and stabilized the binding of RegA to an operator located between the two promoters. The interaction of RegA with its DNA target resulted in the formation of a nucleosome-like structure, which evidently displaced the histone-like proteins, H-NS and StpA, from the adcA and kfc promoter regions, leading to transcriptional derepression. In addition, our results indicated that RegA also behaved as a Class I activator by directly stimulating transcription initiation by RNA polymerase. This is the first report to describe the molecular mechanism by which an environmental chemical stimulates transcription of virulence-associated genes of an enteric pathogen through an AraC/XlyS-like activator.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Artificial Gene Fusion
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Bicarbonates / metabolism*
  • Citrobacter rodentium / genetics
  • Citrobacter rodentium / physiology*
  • DNA Footprinting
  • DNA, Bacterial / metabolism
  • DNA-Binding Proteins / metabolism
  • Electrophoretic Mobility Shift Assay
  • Gene Deletion
  • Gene Expression Regulation, Bacterial*
  • Genes, Reporter
  • Molecular Sequence Data
  • Nucleosomes / metabolism
  • Operator Regions, Genetic
  • Operon*
  • Promoter Regions, Genetic
  • Protein Binding
  • Transcription Initiation Site
  • Transcriptional Activation / drug effects*
  • Virulence Factors / biosynthesis*
  • beta-Galactosidase / genetics
  • beta-Galactosidase / metabolism


  • Bacterial Proteins
  • Bicarbonates
  • DNA, Bacterial
  • DNA-Binding Proteins
  • H-NS protein, bacteria
  • Nucleosomes
  • RegA protein, Bacteria
  • Virulence Factors
  • beta-Galactosidase