Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. This sigma factor regulates the genes for a membrane-located efflux system that confers resistance to nickel and cobalt. CnrH alone is able to activate CNR expression, while both CnrY and CrnX are needed for nickel induction of cnrH (PubMed:10671463). Binds DNA in an RNA polymerase-dependent fashion (PubMed:10671464). CnrH may be controlled by a CnrYX transmembrane anti-sigma factor complex which binds CnrH in the absence of Ni(2+). If Ni(2+) appears in the periplasm, it may be bound by CnrR (CnrX); the signal then would be transmitted by CnrY into the cytoplasm and CnrH would be released. By nickel and cobalt. Belongs to the sigma-70 factor family. ECF subfamily.