Novel RNA polymerase sigma factor from Bacillus subtilis.

A modified form of Bacillus subtilis RNA polymerase (RNA nucleotidyltransferase) has been isolated that exhibits distinctive transcriptional specificity. This modified enzyme transcribes two 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.