The Bacillus subtilis flagellin gene (hag) is transcribed by the sigma 28 form of RNA polymerase.

The Bacillus subtilis gene hag, which codes for the flagellin structural protein, was identified by DNA sequence analysis in a collection of DNA fragments bearing in vitro promoters for the sigma 28 form of RNA polymerase. The hag gene and adjacent regions of the B. subtilis chromosome were restriction mapped, and the nucleotide sequence was determined. The hag gene was transcribed at all stages of growth from a single promoter that had sequences in the promoter recognition region characteristic of the consensus sequence for the sigma 28 holoenzyme. Transcription of hag was eliminated by insertion mutations that blocked synthesis of the sigma 28 protein. These findings provide strong support for the previous proposal that the sigma 28 form of RNA polymerase controls transcription of a regulon specifying flagellar, chemotaxis, and motility functions in B. subtilis (J. D. Helmann and M. J. Chamberlin, Proc. Natl. Acad. Sci. USA 84:6422-6424, 1987). The steady-state levels of hag mRNA increased during exponential growth and peaked as the B. subtilis cells entered the stationary phase. The transcript levels then decreased to zero within 4 h after the onset of sporulation. Hence, sigma 28 RNA polymerase function is temporally regulated.