A redox-regulated anti-sigma factor for extracytoplasmic function (ECF) sigma factor SigR, and a key sensor of disulfide stress. Holds SigR, its cognate ECF sigma factor, in an inactive form, inhibiting its sigma activity under reducing but not oxidizing conditions; oxidation and reduction of the anti-sigma factor is reversible. Mycothiol (MSH) is competent for reduction of RsrA, allowing it to bind to SigR. In conjunction with its cognate sigma factor SigR may sense the intracellular level of reduced MSH. Probably releases SigR during oxidative stress. Binds 1 Zn(2+) per subunit. Zinc is not required for SigR-binding, but is required for anti-sigma factor activity. Zinc-binding renders RsrA relatively resistant to oxidation. Interacts with cognate sigma factor SigR under reducing but not oxiding conditions. Treatment with the thiol-oxidzing agent diamide inhibits the interaction, while incubation with thioredoxin (trxA) stimulates the interaction. Under oxidizing conditions up to 3 disulfide bonds are formed. A single disulfide bond inhibits binding to SigR. Cys-11 forms a disulfide bond with either Cys-44 (the major bind) or Cys-41 (a minor bond). Partially alkylated with iodoacetamide, has 1 disulfide bond. Full alkylated with iodoacetamide. Viable, but defective in sporulation, white color. Strong induction of disulfide reductase (trxB) and thioredoxin-2 (trxC) that is not further induced by diamide. Acts as a SigR constitutive mutant. A double sigR-rsrA mutant sporulates normally but is more sensitive to diamide. A quadruple Cys-3-Ser, Cys-31-Ser, Cys-61-Ala, Cys-62-Ala mutant has anti-sigma factor activity and is induced by diamide. Belongs to the zinc-associated anti-sigma factor (ZAS) superfamily.