Competitive interaction of the OxyR DNA-binding protein and the Dam methylase at the antigen 43 gene regulatory region in Escherichia coli

Mol Microbiol. 2002 Apr;44(2):509-20. doi: 10.1046/j.1365-2958.2002.02905.x.


The antigen 43 surface protein of Escherichia coli is expressed in a phase-variable manner by a mechanism involving alternative activation and repression of transcription of the agn43 gene. The repressor is the OxyR DNA-binding protein, and its binding site was found to be located downstream of the agn43 transcription start site in a region of DNA that encompasses three 5'-GATC-3' sequences that are subject to Dam-mediated DNA methylation. It has been suggested previously that the phase-variable expression of antigen 43 results from a competition between Dam methylase and the OxyR repressor for these sites. The 5'-GATC-3' sequences were inactivated for methylation by site-directed mutagenesis, and all possible combinations of inactive and active sites were assessed for effects on phase-variable expression of the agn43 gene. Inactivation of any 5'-GATC-3' site individually had no effect; at least two sites had to be inactivated to disrupt the normal pattern of expression. Studies of OxyR interaction with agn43 DNA showed that methylation of any two 5'-GATC-3' sites was necessary and sufficient to block binding of the repressor. It was also found that the adenines of the second and third 5'-GATC-3' sites are required for OxyR binding, demonstrating that the sites for Dam methylation and for repressor binding are intimately associated. This is consistent with a competition model in which Dam and OxyR share a preference for specific DNA sequences in the regulatory region of the agn43 gene.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adhesins, Bacterial*
  • Adhesins, Escherichia coli
  • Antigens, Bacterial / genetics
  • Bacterial Outer Membrane Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Codon / genetics
  • DNA Primers
  • DNA-Binding Proteins*
  • Escherichia coli / genetics*
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins*
  • Molecular Sequence Data
  • Regulatory Sequences, Nucleic Acid
  • Repressor Proteins / metabolism*
  • Sequence Alignment
  • Site-Specific DNA-Methyltransferase (Adenine-Specific) / metabolism*
  • Transcription Factors / metabolism*


  • Adhesins, Bacterial
  • Adhesins, Escherichia coli
  • Antigens, Bacterial
  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • Codon
  • DNA Primers
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Repressor Proteins
  • Transcription Factors
  • antigen 43, E coli
  • oxyR protein, E coli
  • Dam methyltransferase
  • Site-Specific DNA-Methyltransferase (Adenine-Specific)
  • dam protein, E coli