A redox-sensitive transcriptional regulator. Maintains intracellular redox homeostasis by regulating catabolic metabolism and polyketide biosynthesis. Regulates expression of the redox buffer ergothioneine (ERG). In concert with myothiol (MSH), another redox buffer, responds to low pH leading to acid resistance. 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. Constitutively expressed. The Fe-S cluster can be nitrosylated by nitric oxide (NO). Upon Fe-S cluster removal intramolecular disulfide bonds are formed. Not essential. Belongs to the WhiB family.