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 (RshA) until released. This sigma factor is involved in heat shock and oxidative stress responses; it positively regulates the expression of itself, sigE, sigB and a number of transcriptional regulators as well as other effectors of heat and oxidative stress, leading to direct and indirect control of up to 25% of the bacterial genome. Modulates expression of host genes for intercrine beta (chemokine CC) and apoptosis, altering the host immune response. 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 (affinity=15 nM) 1:1 (via sigma-70 factor domain-4) with RshA under reducing conditions; the complex is disrupted as temperatures rise. Phosphorylation of RshA decreases its interaction with SigH, leading to increased SigH-mediated transcription. Poorly expressed in exponential phase; induced by heat shock (20-fold, 45 degrees Celsius). Induced 10-fold by the thiol-oxidative agent diamide within 30 minutes of exposure, by 2 hours expression is again normal. Autoregulates its own expression, 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. Phosphorylated, possibly on 2 residues, probably by PknB. Phosphorylation of SigH has no effect on interaction with RshA. Increased susceptibility to oxidative stress (H(2)O(2), cumene hydroperoxide and diamide, PubMed:12123450) and heat shock (45 and 52 degrees Celsius). Loss of stress-induced expression of a number of genes including clpB, dnaK, sigE and trxB (PubMed:11567012), sigB and itself (PubMed:12123450). No effect on infection of human derived macrophages, and murine J774.1 activated and unactivated macrophages (PubMed:12123450). Was identified as a high-confidence drug target. Belongs to the sigma-70 factor family. ECF subfamily.