title: MexR repressor of the mexAB-oprM multidrug efflux operon of Pseudomonas aeruginosa: identification of MexR binding sites in the mexA-mexR intergenic region.
abstract: The MexR repressor of the mexAB-oprM multidrug efflux operon of Pseudomonas aeruginosa was purified as a C-terminal histidine-tagged protein by metal chelate affinity chromatography. The purified protein was shown to bind ca. 200 bp upstream of mexA, at two sites, each of which contains a repeat of the nucleotide sequence GTTGA in inverse orientation. DNA sequence analysis identified mexA and mexR promoters within the MexR binding regions, consistent with the previously observed negative regulation of mexR and mexAB-oprM expression by MexR. Transcription of mexA from the promoter originating within the MexR binding site II was confirmed and shown to be markedly enhanced in a nalB (i.e., mexR) mutant of P. aeruginosa. A second mexA promoter was also identified, ca. 70 bp upstream of mexAB-oprM, and transcription from this promoter appeared to occur in both the wild type and a nalB mutant. Production of MexAB-OprM in wild-type cells may be due to expression from a constitutively expressed proximal promoter, while MexAB-OprM hyperexpression in nalB mutants is due to the additional expression from a MexR-regulated distal promoter.
authors.affiliation: Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, Canada, K7L 3N6.
authors.forename: K
authors.initials: K
authors.lastname: Evans
authors.forename: L
authors.initials: L
authors.lastname: Adewoye
authors.forename: K
authors.initials: K
authors.lastname: Poole
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics*; D021901:DNA, Intergenic; D018432:Drug Resistance, Multiple / Q000235:genetics*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009876:Operon; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D021901:DNA, Intergenic; D026901:Membrane Transport Proteins; C118598:MexA protein, Pseudomonas aeruginosa; C118597:MexB protein, Pseudomonas aeruginosa; C423620:MexR protein, Pseudomonas aeruginosa; C402263:OprM protein, Pseudomonas aeruginosa; D012097:Repressor Proteins