title: Efflux-mediated antiseptic resistance gene qacA from Staphylococcus aureus: common ancestry with tetracycline- and sugar-transport proteins.
abstract: Resistance to intercalating dyes (ethidium, acriflavine) and other organic cations, such as quaternary ammonium-type antiseptic compounds, mediated by the Staphylococcus aureus plasmid pSK1 is specified by an energy-dependent export mechanism encoded by the qacA gene. From nucleotide sequence analysis, qacA is predicted to encode a protein of Mr 55017 containing 514 amino acids. The gene is likely to initiate with a CUG codon, and a 36 bp palindrome immediately preceding qacA, along with an upstream reading frame with homology to the TetR repressors, may be components of a regulatory circuit. The putative polypeptide specified by qacA has properties typical of a cytoplasmic membrane protein, and is indicated to be a member of a transport protein family that includes proteins responsible for export-mediated resistance to tetracycline and methylenomycin, and uptake of sugars and quinate. The analysis suggests that N- and C-terminal regions of these proteins are involved in energy coupling (proton translocation) and substrate transport, respectively. The last common ancestor of the qacA and related tet (tetracycline resistance) lineages is inferred to have been repressor controlled, as occurs for modern tet determinants from Gram-negative, but not those from Gram-positive, bacteria.
authors.affiliation: Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: D A
authors.initials: DA
authors.lastname: Rouch
authors.forename: D S
authors.initials: DS
authors.lastname: Cram
authors.forename: D
authors.initials: D
authors.lastname: DiBerardino
authors.forename: T G
authors.initials: TG
authors.lastname: Littlejohn
authors.forename: R A
authors.initials: RA
authors.lastname: Skurray
mesh_terms: D000595:Amino Acid Sequence; D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D001693:Biological Transport, Active; D050260:Carbohydrate Metabolism; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D003062:Codon; D004269:DNA, Bacterial; D004352:Drug Resistance, Microbial / Q000235:genetics; D015870:Gene Expression; D005798:Genes, Bacterial; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D013211:Staphylococcus aureus / Q000235:genetics*; D013752:Tetracycline / Q000378:metabolism
chemical_list: D000891:Anti-Infective Agents, Local; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003062:Codon; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; C068498:qacA protein, Staphylococcus aureus; D013752:Tetracycline