A redox-regulated anti-sigma factor for cognate extracytoplasmic function (ECF) sigma factor SigH. ECF sigma factors are held in an inactive form by an anti-sigma factor (Probable). Overexpression leads to increased susceptibility to diamide. Binds 1 iron-sulfur cluster per subunit. Interacts with cognate ECF RNA polymerase sigma factor SigH under reducing conditions; the complex is disrupted under oxiding conditions or as temperatures rise. Binding inhibits the interaction of SigH with the RNA polymerase catalytic core. Induced after heat shock (50 degress Celsius). Part of the sigH-rshA operon. Phosphorylated, probably by PknB (Probable). Phosphorylation decreases interaction with SigH, probably leading to increased SigH-mediated transcription. Belongs to the zinc-associated anti-sigma factor (ZAS) superfamily.