A novel operon,
czrAB (zinc-responsible genes), was identified in the chromosome of
Staphylococcus aureus. The operon consists of two genes,
czrA and
czrB. The
czrA gene, coding for an 11.5kDa protein, was homologous to
cadC, arsR of
S. aureus plasmid pI258 and
smtB of
Synechococcus PCC7942. The
czrB, coding for a 36kDa membrane spanning protein, was homologous to the
czcD gene, cobalt, zinc and the cadmium -resistant factor of
Bacillus subtilis and
Alcaligenes eutrophus. In the presence of zinc (0.1-10mM), the transcription of
czrAB was enhanced in a concentration-dependent manner. Other heavy metals, such as cobalt, copper, manganese and nickel showed no effect on
czrAB expression. The disruptant of the
czrB gene became sensitive to zinc ion (MIC, 2mM; MBC, 10mM), and the complementation with the plasmid recovered the resistance to zinc at the same concentration as a parental strain (MIC, 5mM; MBC, 20mM). The disruptant accumulated intracellular zinc up to 0.4mg per g dry weight of the organism, while that of the parental strain was 0.25mg per g dry weight. The findings indicated that the novel operon
czrAB should play a role in the transportation of zinc across the cell membrane to maintain the proper intracellular concentration.
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