Isolation of a Bacillus thuringiensis RNA polymerase capable of transcribing crystal protein genes

We report the isolation of an RNA polymerase from sporulating cells of Bacillus thuringiensis subsp. kurstaki HD-1-Dipel that directs transcription from the promoter region of an insecticidal crystal protein gene. The core components of this RNA polymerase are associated with a polypeptide that has an apparent mass of 35 kDa. Neither RNA polymerase holoenzyme isolated from vegetative B. thuringiensis, nor the core derived from this enzyme, is capable of transcribing from the crystal protein gene promoter region; the addition of gel-purified 35-kDa polypeptide to the core reconstitutes the specific transcribing capability. The reconstituted enzyme does not direct transcription from the promoters for the ctc or spoVG genes of Bacillus subtilis; however, this form of RNA polymerase does direct transcription from a promoter for the 27-kDa crystal protein of B. thuringiensis subsp. israelensis and from a promoter for a 29-kDa polypeptide present in cuboidal crystals of B. thuringiensis subsp. kurstaki HD-1. We propose a tentative consensus sequence based on the alignment of the three B. thuringiensis promoters. This consensus sequence is different from consensus sequences reported for promoters recognized by enzymes containing other sigma subunits, suggesting that the 35-kDa polypeptide is an unusual sigma subunit.