title: QacR is a repressor protein that regulates expression of the Staphylococcus aureus multidrug efflux pump QacA.
abstract: The Staphylococcus aureus QacA protein is a multidrug transporter that confers resistance to a broad range of antimicrobial agents via proton motive force-dependent efflux of the compounds. Primer extension analysis was performed to map the transcription start points of the qacA and divergently transcribed qacR mRNAs. Each gene utilized a single promoter element, the locations of which were confirmed by site-directed mutagenesis. Fusions of the qacA and qacR promoters to a chloramphenicol acetyl transferase reporter gene were used to demonstrate that QacR is a trans-acting repressor of qacA transcription that does not autoregulate its own expression. An inverted repeat overlapping the qacA transcription start site was shown to be the operator sequence for control of qacA gene expression. Removal of one half of the operator prevented QacR-mediated repression of the qacA promoter. Purified QacR protein bound specifically to this operator sequence in DNase I-footprinting experiments. Importantly, addition of diverse QacA substrates was shown to induce qacA expression in vivo, as well as inhibit binding of QacR to operator DNA in vitro, by using gel-mobility shift assays. QacR therefore appears to interact directly with structurally dissimilar inducing compounds that are substrates of the QacA multidrug efflux pump.
authors.affiliation: School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Grkovic
authors.forename: M H
authors.initials: MH
authors.lastname: Brown
authors.forename: N J
authors.initials: NJ
authors.lastname: Roberts
authors.forename: I T
authors.initials: IT
authors.lastname: Paulsen
authors.forename: R A
authors.initials: RA
authors.lastname: Skurray
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D018983:DNA Footprinting; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000502:physiology*; D013211:Staphylococcus aureus / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D012097:Repressor Proteins; C068498:qacA protein, Staphylococcus aureus