title: Competitive interaction of the OxyR DNA-binding protein and the Dam methylase at the antigen 43 gene regulatory region in Escherichia coli.
abstract: 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.
authors.affiliation: Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Republic of Ireland.
authors.forename: Denise E
authors.initials: DE
authors.lastname: Waldron
authors.forename: Peter
authors.initials: P
authors.lastname: Owen
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Dorman
mesh_terms: D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D003062:Codon / Q000235:genetics; D017931:DNA Primers; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000378:metabolism*; D016415:Sequence Alignment; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D003062:Codon; D017931:DNA Primers; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C118376:antigen 43, E coli; C499299:oxyR protein, E coli; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C499294:dam protein, E coli