Gupta S D, Wu H C, Rick P D
Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA.
J Bacteriol. 1997 Aug;179(16):4977-84. doi: 10.1128/jb.179.16.4977-4984.1997.
Three distinct clones from a Salmonella typhimurium genomic library were identified which suppressed the copper-sensitive (Cu(s)) phenotype of cutF mutants of Escherichia coli. One of these clones, pCUTFS2, also increased the copper tolerance of cutA, -C, and -E mutants, as well as that of a lipoprotein diacylglyceryl transferase (lgt) mutant of E. coli. Characterization of pCUTFS2 revealed that the genes responsible for suppression of copper sensitivity (scs) reside on a 4.36-kb DNA fragment located near 25.4 min on the S. typhimurium genome. Sequence analysis of this fragment revealed four open reading frames (ORF120, ORF627, ORF207, and ORF168) that were organized into two operons. One operon consisted of a single gene, scsA (ORF120), whereas the other operon contained the genes scsB (ORF627), scsC (ORF207), and scsD (ORF168). Comparison of the deduced amino acid sequences of the predicted gene products showed that ScsB, ScsC, and ScsD have significant homology to thiol-disulfide interchange proteins (CutA2, DipZ, CycZ, and DsbD) from E. coli and Haemophilus influenzae, to an outer membrane protein (Com1) from Coxiella burnetii, and to thioredoxin and thioredoxin-like proteins, respectively. The two operons were subcloned on compatible plasmids, and complementation analyses indicated that all four proteins are required for the increased copper tolerance of E. coli mutants. In addition, the scs locus also restored lipoprotein modification in lgt mutants of E. coli. Sequence analyses of the S. typhimurium scs genes and adjacent DNAs revealed that the scs locus is flanked by genes with high homology to the cbpA (predicted curved DNA-binding protein) and agp (acid glucose phosphatase) genes of E. coli located at 22.90 min (1,062.07 kb) and 22.95 min (1,064.8 kb) of the E. coli chromosome, respectively. However, examination of the E. coli chromosome revealed that these genes are absent at this locus and no evidence has thus been obtained for the occurrence of the scs locus elsewhere on the genome.
从鼠伤寒沙门氏菌基因组文库中鉴定出三个不同的克隆，它们抑制了大肠杆菌cutF突变体的铜敏感（Cu(s)）表型。其中一个克隆pCUTFS2，还提高了cutA、-C和-E突变体以及大肠杆菌脂蛋白二酰甘油转移酶（lgt）突变体的耐铜性。对pCUTFS2的表征显示，负责抑制铜敏感性（scs）的基因位于鼠伤寒沙门氏菌基因组上25.4分钟附近的一个4.36 kb DNA片段上。对该片段的序列分析揭示了四个开放阅读框（ORF120、ORF627、ORF207和ORF168），它们被组织成两个操纵子。一个操纵子由单个基因scsA（ORF120）组成，而另一个操纵子包含scsB（ORF627）、scsC（ORF207）和scsD（ORF168）基因。对预测基因产物推导的氨基酸序列进行比较表明，ScsB、ScsC和ScsD分别与大肠杆菌和流感嗜血杆菌的硫醇-二硫键交换蛋白（CutA2、DipZ、CycZ和DsbD）、伯氏考克斯氏体的外膜蛋白（Com1）以及硫氧还蛋白和硫氧还蛋白样蛋白具有显著同源性。这两个操纵子被亚克隆到相容质粒上，互补分析表明，所有四种蛋白质都是大肠杆菌突变体提高耐铜性所必需的。此外，scs基因座还恢复了大肠杆菌lgt突变体中的脂蛋白修饰。对鼠伤寒沙门氏菌scs基因和相邻DNA的序列分析表明，scs基因座两侧分别是与大肠杆菌位于染色体22.90分钟（1,062.07 kb）和22.95分钟（1,064.8 kb）处的cbpA（预测的弯曲DNA结合蛋白）和agp（酸性葡萄糖磷酸酶）基因具有高度同源性的基因。然而，对大肠杆菌染色体的检查表明，该基因座上不存在这些基因，因此没有获得该scs基因座在基因组其他位置出现的证据。
