Isolation and physical mapping of the gene encoding the major sigma factor of Bacillus subtilis RNA polymerase.

At least four sigma factors separately bind the Bacillus subtilis RNA polymerase core (beta beta' alpha 2), each conferring a different promoter specificity on the holoenzyme in vitro. Using the Broome-Gilbert immunological screening, we isolated recombinant lambda phages that carry rpoD, the gene for the most abundant sigma factor, sigma 55. These phages encode a 55,000-dalton protein whose size, immunological properties, and peptide map identify it as sigma 55. All the phages have in common two adjacent 3.5-kilobase EcoRI fragments from the B. subtilis chromosome; most carry additional genomic DNA. Deletion analysis localized rpoD to a 1.6-kilobase region, suggested the direction of its transcription, and found two additional genes near rpoD, which code for proteins of 62,000 and 17,000 daltons.