Sigma factors are initiation factors that promote the attachment of RNA polymerase (RNAP) 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 (YhdL) until released (PubMed:14993308). This sigma factor is involved in the maintenance of membrane and cell wall integrity in response to environmental stresses including salt, acid, ethanol and antibiotics stress (PubMed:22211522, PubMed:12775685). Partially regulates transcription from a number of genes including disA (PubMed:17434969). Associates with RNAP core under all growth phases (PubMed:21710567). Interacts with the N-terminus of YhdL, which is probably its anti-sigma factor (PubMed:14993308). Interacts transiently with the RNAP core (Probable). Forms an operon with yhdL and yhdK, maximally expressed during early to mid-exponential growth phases (PubMed:10216858). Transcription decreases during late exponential growth; positively autoregulated (PubMed:10216858). Negatively regulated by yhdL and yhdK (PubMed:10216858). Induced by 5% ethanol, 80 uM paraquat, pH 4.3, the antibiotics, inhibitors of cell wall, bacitracin, vancomycin and phosphomycin, heat shock of 10 minutes at 50 degrees Celsius (PubMed:12775685). No induction was observed with pH 9, H(2)O(2), monensin, and the detergents Triton X-100 and Tween 20 (PubMed:12775685). Induced 3-fold by the beta-lactam antibiotic cefuroxime (PubMed:22211522). Strains insertionally inactivated in the sigM gene form aberrantly shaped cells that swell and lyse in medium containing high levels of different salts (PubMed:10216858). 70-fold increased sensitivity to the beta-lactam antibiotic cefuroxime (CEF), double sigM-sigX mutants have 130-fold increased sensitivity to CEF (PubMed:22211522). Also sensitive to other antibiotics (PubMed:22211522). Belongs to the sigma-70 factor family. ECF subfamily.