Acts as a transcriptional regulator. Probably redox-responsive. The apo- but not holo-form probably binds DNA (By similarity). Binds 1 [4Fe-4S] cluster per subunit. Following nitrosylation of the [4Fe-4S] cluster binds 1 [4Fe-8(NO)] cluster per subunit. Weakly expressed in exponential phase, expression peaks as cells enter stationary phase then falls again. 30-fold induced by iron-starvation, 60-fold by heat shock, 70-fold by streptomycin and kanamycin. 2-fold repressed by ethanol and streptomycin. Slightly induced during entry into hypoxia, by NO, cAMP, in mouse infections and 15-fold induced in macrophage infection. The Fe-S cluster can be nitrosylated by nitric oxide (NO). Upon Fe-S cluster removal intramolecular disulfide bonds are formed. Belongs to the WhiB family. Extended N-terminus.