Acts as a transcriptional regulator. Probably redox-responsive. The apo- but not holo-form probably binds DNA (By similarity). Complements a whiB2 disruption mutant in M.smegmatis (AC Q9S426). Binds 1 [4Fe-4S] cluster per subunit. Following nitrosylation of the [4Fe-4S] cluster binds 1 [4Fe-8(NO)] cluster per subunit. Transcribed from 2 promoters; expression from the stronger promoter is induced when aerial hyphae became visible and then declines. Expressed during exponential growth but decreases during stationary phase in liquid culture. The Fe-S cluster can be nitrosylated by nitric oxide (NO). Upon Fe-S cluster removal intramolecular disulfide bonds are formed. A white non-sporulating phenotype. Spore septation does not occur. Belongs to the WhiB family.