The furA-katG region of Mycobacterium tuberculosis, encoding a Fur-like protein and the catalase-peroxidase, is highly conserved among mycobacteria. Both genes are induced upon oxidative stress. In this work we analyzed the M. tuberculosis furA promoter region. DNA fragments were cloned upstream of the luciferase reporter gene, and promoter activity in Mycobacterium smegmatis was measured in both the presence and absence of oxidative stress. The shortest fragment containing an inducible promoter extends 45 bp upstream of furA. In this region, ؊35 and ؊10 promoter consensus sequences can be identified, as well as a 23-bp AT-rich sequence that is conserved in the nonpathogenic but closely related M. smegmatis. M. tuberculosis Fur-like proteins are widespread in both gram-negative and gram-positive bacteria. Their major role in the regulation of iron uptake systems in response to environmental iron was first described for Escherichia coli (for a review, see reference 14). Under iron-replete conditions, the Fur protein, using Fe 2ϩ as a corepressor, binds to a 19-bp operator sequence located upstream of the Fur-regulated genes (2, 10, 11, 13).Fur and Fur-like proteins were found to be involved in regulation of functions as varied as the acid shock response (17), detoxification of oxygen radicals (12, 18), production of toxins and virulence factors (20, 31), and metabolic pathways (24, 29). These observations led Fur-like proteins to be considered not only transcriptional repressors but also global regulators.The E. coli Fur protein (17 kDa) contains a nonclassical helix-turn-helix DNA binding domain and is active as a homodimer (7). In vivo assays showed that the N-terminal domain is involved in DNA binding and that the C-terminal domain is involved in dimerization (29). Biochemical analysis indicated that repressor activation occurs upon a conformational change due to metal binding to the C-terminal domain (8,15,30). The Fur protein contains two metal ion binding sites: the iron binding regulatory site and a tightly binding zinc site that plays a role in stability of the protein (1, 19).Several redox-sensing proteins of the Fur family have been identified in various bacteria. Their role in the oxidative stress response might be mediated via metal-catalyzed oxidation of the protein or a change in the oxidation state of the bound metal ion (4, 16). This is the case for CatR in Streptomyces coelicolor, which regulates its own gene and the catalase CatA by binding to operator sequences upstream of their promoters under reducing conditions (16). Similarly, in Streptomyces reticuli, FurS in the thiol-reduced form specifically binds to a motif upstream of the furS gene (25).The furA gene has been identified in Mycobacterium tuberculosis as well as other mycobacterial species (6,23,26). S. reticuli FurS and M. tuberculosis FurA show 53% identity, and the predicted secondary structures of the two proteins are similar. Moreover, typical motifs involved in metal binding and several cysteines that may sense the oxidative stres...