Sigma factors are initiation factors that promote the attachment of RNA polymerase (RNAP) to specific initiation sites and are then released. Sigma-W controls genes involved in response to cell envelope stress such as antimicrobial peptides (PubMed:12207695, PubMed:15870467), alkaline pH (PubMed:11454200), transport processes and detoxification. Extracytoplasmic function (ECF) sigma factors are held in an inactive form by a cognate anti-sigma factor (RsiW for this protein) until released by regulated membrane proteolysis (RIP). RIP occurs when an extracytoplasmic signal (envelope stress) triggers a concerted proteolytic cascade to transmit information and elicit cellular responses. The anti-sigma factor RsiW is a membrane protein, binding sigma-W in the cytoplasm. RsiW is first cut extracytoplasmically (site-1 protease, S1P, by PrsW) (PubMed:16816000), then within the membrane itself (site-2 protease, S2P, by RasP) (PubMed:15130127), while cytoplasmic proteases (predominantly ClpX-ClpP) finish degrading the regulatory protein, liberating sigma-W (PubMed:16899079). 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. Forms a heterodimer with cognate anti-sigma factor RsiW, which prevents it binding to the -10 and -35 promoter elements (PubMed:28319136). By different stresses causing damage to the cell envelope, such as alkaline shock (PubMed:11454200), salt shock (PubMed:11544224), phage infection and certain antibiotics that affect cell wall biosynthesis (PubMed:12207695, PubMed:15870467). Does not respond to oxidative stress caused by diamide (PubMed:21685450). Association with RNAP core increases during most stresses but not during sporulation (at protein level) (PubMed:21710567). The sigma-70 factor domain-2 mediates sequence-specific interaction with the -10 element in promoter DNA (PubMed:28319136), and plays an important role in melting the double-stranded DNA and the formation of the transcription bubble. Also 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 (PubMed:28319136). The domain also mediates interaction with the RNA polymerase subunit RpoA (By similarity). Alteration (reduction or loss for the most part) of expression of about 60 genes that are high-pH-inducible, including sigW and its anti-sigma factor rsiW (PubMed:11454200). Belongs to the sigma-70 factor family. ECF subfamily.