Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. This sigma factor controls the expression of flagella-related genes. 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). Mutants have poor biofilms (decrease in biomass, surface coverage and mean thickness). The distinguishing feature of FliA promoters is a long -10 region (GCCGATAA). The upstream GC constitutes an extended -10 motif and is recognized by Arg-91 (PubMed:19400790). Belongs to the sigma-70 factor family. FliA subfamily.