Acts as a transcriptional regulator. Probably redox-responsive. The apo- but not holo-form probably binds DNA (By similarity). The apo-form has been shown to act as a protein disulfide reductase. Binds 1 [4Fe-4S] cluster per subunit. Contains 1 [2Fe-2S] cluster after reconstitution of overexpressed protein from E.coli. Following nitrosylation of the [4Fe-4S] cluster binds 1 [4Fe-8(NO)] cluster per subunit. Weakly expressed in exponential phase, more induced upon entry into stationary phase. 3-fold induced by streptomycin and pH 4.5, 4-fold by ethanol. Slightly induced during entry into hypoxia, by cAMP, in macrophage infection and 5-fold induced by NO. Repressed by WhiB4. The Fe-S cluster can be nitrosylated by nitric oxide (NO). Upon Fe-S cluster removal intramolecular disulfide bonds are formed. Fully oxidized recombinant protein tagged at both termini. Fully reduced recombinant protein tagged at both termini. Belongs to the WhiB family.