An anti-sigma factor for extracytoplasmic function (ECF) sigma factor sigma-F (SigF), which responds to chromate and cadmium. Overexpression leads to loss of response to dichromate. ECF sigma factors are held in an inactive form by a cognate anti-sigma factor (Probable). Slightly induced by potassium dichromate (K(2)Cr(2)O(7)) (PubMed:22985357). Induction by Cr is partially dependent on sigF (PubMed:22985357). Probably part of the sigF-nrsF operon (PubMed:22985357). Cannot be deleted in the presence of an intact sigF gene, a double sigF-nrsF mutant is viable. Belongs to the NrsF anti-sigma-F factor family.