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 usually held in an inactive form by an anti-sigma factor until released by regulated intramembrane proteolysis; this sigma factor does not seem to have a cognate anti-sigma factor however. It has been suggested that the sigma domains 2 and 4 may interact via polar residues in this protein to autoregulate. Positively regulates expression of a small regulon of genes. 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. The most abundant of the sigma factor transcripts, it is expressed in exponential phase; repressed by detergent (7-fold), heat shock (9-fold, 45 degrees Celsius) and in stationary phase. Not autoregulated (PubMed:22015173). 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 (By similarity). No effect on growth in culture, or in isolated macrophages; infected guinea pigs have a highly attenuated infection with few granulomas and no necrotic centers. Was identified as a high-confidence drug target. Belongs to the sigma-70 factor family. ECF subfamily. The protein has been shown to be 126 residues longer (PubMed:17145760), but in (PubMed:19118359) no evidence of this longer protein was seen.