We describe a mutation that changes the fine specificity of promoter selection by a secondary form of RNA polymerase holoenzyme in Bacillus subtilis. The product of regulatory gene spo0H is an RNA polymerase sigma factor called σH, which directs transcription of a sporulation gene known as spoVG. We show that the spo0H mutation spo0H81, which blocks transcription from the wild-type spoVG promoter, enhances transcription from a mutant form of the spoVG promoter (spoVG249) bearing a severe down-mutation (a G · C to A · T transition) at position -13 in the "-10 region." Suppression of the spoVG249 mutation is specific in the sense that the transcription from several other spoVG mutant promoters was not restored by the mutant sigma. Evidently, spo0H81 is a change-of-specificity mutation that alters σH-RNA polymerase in a way that decreases its capacity to use the wild-type spoVG promoter, while increasing its capacity to use the mutant promoter. Transcription experiments in vitro using RNA polymerase containing the wild-type or mutant sigma support this interpretation. The spo0H81 mutation causes a threonine (Thr100) to isoleucine substitution in a region of σH that is highly homologous among sigma factors of diverse origins. We discuss the possibility that Thr100 is an amino acid-base-pair contact site and that sigma factors contact the -10 region of their cognate promoters by means of amino acid residues in this highly conserved region.
|Original language||English (US)|
|Number of pages||10|
|Journal||Journal of molecular biology|
|State||Published - Apr 20 1989|
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology