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 an anti-sigma factor until released. This sigma factor is involved in heat shock and oxidative stress responses. Interacts transiently with the RNA polymerase catalytic core formed by RpoA, RpoB, RpoC and RpoZ (2 alpha, 1 beta, 1 beta' and 1 omega subunit) to form the RNA polymerase holoenzyme that can initiate transcription. Interacts (via sigma-70 factor domain-4) with anti-sigma-H factor RshA, probably under reducing conditions, which prevents its interaction with RNA polymerase. Expressed at low levels at 37 degrees Celsius; 5-fold further induced after heat shock (50 degress Celsius). A longer form is transiently induced by diamide (at protein level). Autoregulated. Part of the sigH-rshA operon. The sigma-70 factor domain-2 mediates sequence-specific interaction with the -10 element in promoter DNA, and plays an important role in melting the double-stranded DNA and the formation of the transcription bubble. The sigma-70 factor domain-2 mediates interaction with the RNA polymerase subunits RpoB and RpoC (By similarity). The sigma-70 factor domain-4 contains a helix-turn-helix (H-T-H) motif that mediates interaction with the -35 element in promoter DNA. The domain also mediates interaction with the RNA polymerase subunit RpoA. Interactions between sigma-70 factor domain-4 and anti-sigma factors prevents interaction of sigma factors with the RNA polymerase catalytic core (By similarity). Increased sensitivity to cumene hydroperoxide but not H(2)O(2) (PubMed:10400584). Increased sensitivity to the oxidant diamide (PubMed:14617153). Constitutively expressed major isoform, not induced by diamide, after 60 minutes diamide no longer present (at protein level). Transiently produced upon diamide induction. The longer form is seen in gels but the actual sequence is unproven. Belongs to the sigma-70 factor family. ECF subfamily. Extended N-terminus.