FIG 8 .

A model of zinc homeostasis in Salmonella Typhimurium. Under conditions of zinc deficiency, zinc is not available to bind to the Zur repressor, leading to expression of the ZnuABC zinc acquisition system. ZupT, whose regulation is uncharacterized, has also been shown to contribute to zinc acquisition. When zinc is abundant, Zur bound to zinc represses ZnuABC expression. In addition, free cytoplasmic zinc binds to the transcriptional activator ZntR to induce expression of the ZntA zinc efflux system. Zinc efflux in S. Typhimurium is also mediated by ZitB. Under conditions of nitrosative stress, S-nitrosylation of cysteine ligands in zinc metalloproteins leads to mobilization of free intracellular zinc. The zinc efflux activities of ZntA and ZitB are required for the resistance of S. Typhimurium to nitrosative stress.