Acts as a transcriptional regulator. Probably redox-responsive. The apo- but not holo-form probably binds DNA (By similarity). Plays a role in lipooligosaccharide (LOS) biosynthesis by regulating LOS gene expression. Binds 1 [4Fe-4S] cluster per subunit. Following nitrosylation of the [4Fe-4S] cluster binds 1 [4Fe-8(NO)] cluster per subunit. The Fe-S cluster can be nitrosylated by nitric oxide (NO). Upon Fe-S cluster removal intramolecular disulfide bonds are formed. Has a rough-dry colony morphology. About 50% lipooligosaccharide (LOS) biosynthesis, with LOS-III and LOS-IV being most affected. Decreased expression of a number of genes involved in LOS synthesis, such as mmar_2326, mmar_2327, mmar_2354 and papA3 (mmar_2355). Belongs to the WhiB family.