title: Functional characterization of a cadmium resistance operon in Staphylococcus aureus ATCC12600: CadC does not function as a repressor.
abstract: Sequencing of a cadmium resistance operon from a Staphylococcus aureus ATCC12600 plasmid revealed that it is identical to a cadCA operon found in MRSA strains. Compared to plasmid-cured and cadC-mutant strains, cadC-positive ATCC12600 cells had increased resistance to cadmium (1 mg ml(-1) cadmium sulfate) and zinc (4 mg ml(-1) zinc sulfate), but not to other metal ions. After growth in media containing 20 µg ml(-1) cadmium sulfate, cadC-mutant cells contained more intracellular cadmium than cadC-positive ATCC12600 cells, suggesting that cadC absence results in impaired cadmium efflux. Electrophoretic mobility shift assays were performed with CadC proteins encoded by the S. aureus ATCC12600 plasmid and by the cadC gene of pI258, which is known to act as a transcriptional repressor and shares only 47% protein sequence identity with ATCC12600 CadC. Mobility shifts occurred when pI258 CadC protein was incubated with the promoter DNA-regions from the pI258 and S. aureus ATCC12600 cadCA operons, but did not occur with S. aureus ATCC12600 CadC protein, indicating that the ATCC12600 CadC protein does not interact with promoter region DNA. This cadCA operon, found in MRSA strains and previously functionally uncharacterized, increases resistance to cadmium and zinc by an efflux mechanism, and CadC does not function as a transcriptional repressor.
authors.affiliation: Calvin College Departments of Biology, Knollcrest Circle SE, Grand Rapids, MI, USA.
authors.forename: Arlene J
authors.initials: AJ
authors.lastname: Hoogewerf
authors.forename: Lisa A Van
authors.initials: LA
authors.lastname: Dyk
authors.forename: Tyler S
authors.initials: TS
authors.lastname: Buit
authors.forename: David
authors.initials: D
authors.lastname: Roukema
authors.forename: Emily
authors.initials: E
authors.lastname: Resseguie
authors.forename: Christina
authors.initials: C
authors.lastname: Plaisier
authors.forename: Nga
authors.initials: N
authors.lastname: Le
authors.forename: Lee
authors.initials: L
authors.lastname: Heeringa
authors.forename: Douglas A Vander
authors.initials: DA
authors.lastname: Griend
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004587:Electrophoresis, Agar Gel; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics / Q000502:physiology; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; C080050:CadC protein, Bacteria; D012097:Repressor Proteins; D002104:Cadmium; D015032:Zinc
keywords: CadC; Cadmium efflux system accessory protein; Cadmium resistance; Heavy metal resistance; Staphylococcus aureus