IDENTIFICATION AND CHARACTERIZATION OF SNQ2, A NEW MULTIDRUG ATP BINDING CASSETTE TRANSPORTER OF THE YEAST PLASMA-MEMBRANE

The SNQ2 gene of Saccharomyces cerevisiae, which encodes an ATP bindin g cassette protein responsible for resistance to the mutagen 4-nitroqu inoline oxide, is regulated by the DNA-binding proteins PDR1 and PDR3. In a plasma membrane-enriched fraction from a pdr1 mutant, the SNQ2 p rotein is found in the 160-kDa over-expressed band, together with PDR5 . The SNQ2 protein was solubilized with n-dodecyl beta-D-maltoside fro m the plasma membranes of a PDR5-deleted strain and separated from the PMA1 H+-ATPase by sucrose gradient centrifugation. The enzyme shows a nucleoside triphosphatase activity that differs biochemically from th at of PDR5 (Decottignies, A., Kolaczkowski, M., Balzi, E., and Goffeau , A. (1994) J. Biol. Chem. 269, 12797-12803) and is sensitive to vanad ate, erythrosine B, and Triton X-100 but not to oligomycin, which inhi bits the PDR5 activity only. Disruption of both PDR5 and SNQ2 in a pdr 1 mutant decreases the cell growth rate and reveals the presence of at least two other ATP binding cassette proteins in the 160-kDa overexpr essed band that have been identified by amino-terminal microsequencing .