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Efflux‐mediated antiseptic resistance gene qacA from Staphylococcus aureus : common ancestry with tetracycline‐ and sugar‐transport proteins
Author(s) -
Rouch D. A.,
Cram D. S.,
Berardino D.,
Littlejohn T. G.,
Skurray R. A.
Publication year - 1990
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1990.tb00565.x
Subject(s) - biology , tetr , efflux , tetracycline , microbiology and biotechnology , lanthionine , genetics , gene , operon , staphylococcus aureus , major facilitator superfamily , acriflavine , repressor , biochemistry , amino acid , bacteria , escherichia coli , gene expression , mutant , antibiotics
Summary Resistance to intercalating dyes (ethidium, acriflavine) and other organic cations, such as quaternary ammonium‐type antiseptic compounds, mediated by the Staphylococcus aureus ptasmid 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 M r 55017 containing 514 amino acids. The gene is likely to initiate with a CUG codon, and a 36bp 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 reponsible 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.