Sigma factors are initiation factors that promote the attachment of RNA polymerase (RNAP) to specific initiation sites and are then released. This alternative sigma factor is required for the transcription of the flagellin and motility genes as well as for wild-type chemotaxis. Associates with the RNAP core during all growth phases with a peak at the transition to stationary phase (PubMed:21710567). Monomer (PubMed:7602586). Interacts transiently with the RNAP core (Probable). Association with RNAP core increases during H(2)O(2), NaOH, rifampicin stress and during sporulation (at protein level). Belongs to the sigma-70 factor family.