Redox-responsive transcriptional regulator that regulates a set of genes involved in protection against environmental stresses encountered during infection. The loss of the O(2) and NO-responsive 4Fe-4S cluster and subsequent redox modifications of Cys residue thiols (possibly by disulfide bond formation) may activate its role in gene regulation. The thiol-oxidized apo-form binds in a sequence non-specific manner to GC-rich DNA, probably in the minor groove. Represses transcription of a number of genes including itself. The reduced apo-form and holo-form do not bind DNA. The apo-form can act as protein disulfide reductase