Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. Extracytoplasmic function (ECF) sigma factors are held in an inactive form by a cognate anti-sigma factor (NrsF in this case) until they are released (Probable). Up-regulates expression of 4 operons (sigF-nrsF, CCNA_02834, CCNA_03001 to CCNA_02999 and CCNA_03363 to CCNA_03366) in response to potassium dichromate (K(2)Cr(2)O(7)) or cadmium chloride (CdCl(2)) (PubMed:22985357). Overexpression of sigF leads to higher expression of its regulon (PubMed:22985357). Tightly associated with the inner membrane via NrsF, upon dichromate stress a small proportion is released to the cytoplasm. Mutation of 2 conserved Cys residues in anti-sigma factor NrsF leads to more SigF in the cytoplasm and greater release upon dichromate stress (PubMed:22985357). Slightly induced by dichromate, partially dependent in itself for expression, does not depend on sigT or sigE. Probably part of the sigF-nrsF operon (PubMed:22985357). Not essential even when cells grown in the presence of dichromate or cadmium (CdCl(2)). Loss of dichromate and cadmium induction of the regulon's genes, including partial loss of its own expression. A double sigF-nrsF deletion is viable, whereas a single nrsF deletion (for the cognate anti-sigma factor) cannot be made. Belongs to the sigma-70 factor family. ECF subfamily.