Copper ion is an essential micronutrient but it is also extremely cytotoxic when it exists in excess. Our stud-ies have shown that Salmonella enterica serovar Ty-phimurium can survive potentially lethal copper expo-sures by the way of copper efflux system. A copper ion inducible gene was identified in virulent S. typhi-murium by using the technique of MudJ (Km, lac)-directed lacZYA operon fusions. A copper ion induc-ible strain LF153 (cuiD::MudJ) has been identified. The cuiD mutant exhibits a copper sensitive phenotype but possesses normal resistance to other metal ions, and lost DMP oxidase activity. Therefore, we suggest that cuiD is an important gene for copper homeostasis and the copper resistance response. The copper sensi-tive phenotype was complemented by pYL3.0 carrying cuiD+. Sequence analysis showed cuiD contains 1,614 bp encoding a 536 amino acid with a 27 amino acid signal peptide and a 509 amino acid residues compris-ing the mature peptide. The CuiD shows 81% homol-ogy to YacK, a putative multicopper oxidases which extrudes copper in Escherichia coli. This ORF con-tains four conserved regions that contain 12 copper ligands (types 1, 2, and 3) present in various copper homeostasis responsible proteins. The H2O2 sensitive phenotype of the cuiD mutant indicates that cuiD may be involved in oxidative stress response.

Keywords: Multicopper Oxidase, S, Copper Homeostasis, Copper