Kuroda M, Hayashi H, Ohta T
Department of Microbiology, Institute of Basic Medical Sciences, and College of Medical Technology, University of Tsukuba, Ibaraki, Japan.
Microbiol Immunol. 1999;43(2):115-25. doi: 10.1111/j.1348-0421.1999.tb02382.x.
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 11.5 kDa protein, was homologous to cadC, arsR of S. aureus plasmid pI258 and smtB of Synechococcus PCC7942. The czrB, coding for a 36 kDa 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 (0.1-10 mM), 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, 2 mM; MBC, 10 mM), and the complementation with the plasmid recovered the resistance to zinc at the same concentration as a parental strain (MIC, 5 mM; MBC, 20 mM). The disruptant accumulated intracellular zinc up to 0.4 mg per g dry weight of the organism, while that of the parental strain was 0.25 mg 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.
在金黄色葡萄球菌染色体中鉴定出一个新的操纵子czrAB（锌相关基因）。该操纵子由两个基因czrA和czrB组成。czrA基因编码一种11.5 kDa的蛋白质，与金黄色葡萄球菌质粒pI258的cadC、arsR以及聚球藻PCC7942的smtB同源。czrB基因编码一种36 kDa的跨膜蛋白，与枯草芽孢杆菌和真养产碱菌的czcD基因、钴、锌和镉抗性因子同源。在锌（0.1 - 10 mM）存在的情况下，czrAB的转录以浓度依赖的方式增强。其他重金属，如钴、铜、锰和镍对czrAB的表达没有影响。czrB基因的缺失突变体对锌离子变得敏感（MIC，2 mM；MBC，10 mM），用质粒互补可恢复与亲本菌株相同浓度的锌抗性（MIC，5 mM；MBC，20 mM）。缺失突变体积聚细胞内锌高达每克生物体干重0.4毫克，而亲本菌株为每克干重0.25毫克。这些发现表明，新的操纵子czrAB在锌跨细胞膜运输以维持适当的细胞内浓度方面应发挥作用。
