Mutation changing the specificity of an RNA polymerase sigma factor.
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 sigma H, 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 sigma H-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 sigma H 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.
Zuber
P
P
Department of Cellular and Developmental Biology, Harvard University, Cambridge, MA 02138.
Healy
J
J
Carter
H L
HL
Cutting
S
S
Moran
C P
CP
Losick
R
R
D001412:Bacillus subtilis / Q000235:genetics; D001483:Base Sequence; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D005798:Genes, Bacterial; D007763:Lac Operon; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D012808:Sigma Factor / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D012808:Sigma Factor; D014157:Transcription Factors; D012321:DNA-Directed RNA Polymerases