Gene encoding sigma E is transcribed from a sigma A-like promoter in Bacillus subtilis

Abstract

Bacillus subtilis produces several RNA polymerase sigma factors. At least two of these factors are essential for endospore formation, sigma H, which is present in vegetative cells, and sigma E, which is produced exclusively after the start of endospore formation. The structural gene that encodes sigma E is part of the spoIIG operon, which is transcribed after the onset of sporulation. We have determined the starting point of transcription and the nucleotide sequence of the spoIIG promoter. This promoter contains sequences that are similar to those found at the -10 and -35 regions of promoters that are used by E sigma A, the primary form of RNA polymerase in vegetative cells. The unusual feature of this promoter is that these putative sigma A contact sites are separated by 22 base pairs, rather than the typical 17 or 18 base pairs. Single-base substitutions in the -10-like sequence reduced utilization of the spoIIG promoter in vivo. Furthermore, E sigma A, but not E sigma H and other secondary forms of RNA polymerase, accurately initiated transcription from the spoIIG promoter in an in vitro assay; therefore, we suggest that E sigma A transcribes the spoIIG operon in vivo. A base substitution in the -35-like sequence caused constitutive transcription from the promoter in vegetative cells; therefore, regulation of this sporulation-specific transcription may involve a novel mechanism.