QACR IS A REPRESSOR PROTEIN THAT REGULATES EXPRESSION OF THE STAPHYLOCOCCUS-AUREUS MULTIDRUG EFFLUX PUMP QACA

The Staphylococcus aureus QacA protein is a multidrug transporter that confers resistance to a broad range of antimicrobial agents via proto n motive force dependent efflux of the compounds. Primer extension ana lysis was performed to map the transcription start points of the qacA and divergently transcribed qacR mRNAs. Each gene utilized a single pr omoter element, the locations of which were confirmed by site-directed mutagenesis. Fusions of the qacA and qacR promoters to a chlorampheni col acetyl transferase reporter gene were used to demonstrate that Qac R is a trans-acting repressor of qacA transcription that does not auto regulate its own expression. An inverted repeat overlapping the qacA t ranscription start site was shown to be the operator sequence for cont rol of qacA gene expression. Removal of one half of the operator preve nted QacR-mediated repression of the qacA promoter. Purified QacR prot ein bound specifically to this operator sequence in DNase I-footprinti ng experiments. Importantly, addition of diverse QacA substrates was s hown to induce qacA expression in vivo, as well as inhibit binding of QacR to operator DNA in vitro, by using gel-mobility shift assays. Qac R therefore appears to interact directly with structurally dissimilar inducing compounds that are substrates of the QacA multidrug efflux pu mp.