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. Essentially constitutive during exponential and early stationary phases, decreases in late stationary phase. 3-fold induced by starvation, 3-fold by cumene hydroperoxide and 5-fold by diamide (oxidzing agents), 15-fold induced by SDS, 200-fold by heat shock. Repressed by SDS and diamide. Not induced by hypoxia, NO, cAMP or in mouse infection, slightly repressed 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.