Acts as a transcriptional repressor, inhibiting expression in vitro. Probably redox-responsive. The apo- but not holo-form binds to its own promoter as well as that of groEL2. Oxidized apo-form and nitrosylated holo-form also bind DNA. The apo-form has been shown to act as a protein disulfide reductase (PubMed:17157031) (PubMed:19016840), but also not to act as a protein disulfide reductase (PubMed:20929442). Binds 1 [4Fe-4S] cluster per subunit. This cluster is stable to O(2) but very reactive to nitric oxide (NO). Following nitrosylation of the [4Fe-4S] cluster binds 1 [4Fe-8(NO)] cluster per subunit. E(0) is -236 +/-2 mV. Homodimer. Interacts with GlgB via an intermolecular disulfide bond. Activated by CRP. Essentially constitutive over all growth phases. 2-fold induced by ethanol, repressed by SDS and heat shock. Not induced by hypoxia, slightly induced by NO and in macrophage and mouse infection, 10-fold induced by cAMP. There are 2 CRP-binding sites in the promoter of whiB1, at low concentrations of CRP with or without cAMP transcription of whiB1 is enhanced via site CRP1, then repressed as site CRP2 is filled. Can be nitrosylated by NO, 8 NO react per cluster leading to the formation of 2 dinitrosyliron thiol complexes (DNIC). These complexes are quite stable in the presence of air. Upon aerobic 4Fe-4S cluster removal intramolecular disulfide bonds are formed. Fully oxidized recombinant protein tagged at both termini. For fully alkylated recombinant protein tagged at both termini. Essential. Belongs to the WhiB family.