Novel RNA polymerase sigma factor from Bacillus subtilis.

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Abstract
A modified form of B. subtilis RNA polymerase (RNA nucleotidyltransferase) was isolated that exhibits distinctive transcriptional specificity. This modified enzyme transcribes 2 cloned genes from the purA-cysA region of the B. subtilis chromosome whose expression in vivo is associated with the process of sporulation. Neither of these genes is transcribed by the usual form of B. subtilis RNA polymerase holoenzyme containing a .sigma. factor of 55,000 daltons (.sigma.55). The modified RNA polymerase lacks .sigma.55 but contains a newly identified subunit of 37,000 daltons termed .sigma.37. A reconstitution experiment in which .sigma.37 was added to core RNA polymerase strongly suggests that .sigma.37 is responsible for the transcriptional specificity of the modified RNA polymerase. .sigma.37 apparently acts at the level of promoter recognition; this transcriptional determinant enabled core RNA polymerase to form stable binary and ternary (initiation) complexes with endonuclease restriction fragments containing promoters for the cloned B. subtilis genes.