A NOVEL BACTERIAL TRANSCRIPTION CYCLE INVOLVING SIGMA(54)

sigma(54) is the promoter recognition subunit of the form of bacterial RNA polymerase that transcribes from promoters with enhancer elements . DNase footprinting experiments show that sigma(54) is attached selec tively to the template strand, which must be single-stranded for trans cription initiation. sigma(54) remains bound at the promoter after cor e polymerase begins elongation, in contrast to the well-established si gma(70)-holoenzyme transcription cycle. Permanganate footprinting expe riments show that the bound sigma(54) and the elongating core RNA poly merase downstream of it are each associated with a single-stranded DNA region. Template commitment assays show that the promoter-bound sigma (54) must be reconfigured before reinitiation of transcription can occ ur. This unexpected pathway raises interesting possibilities for trans criptional regulation, especially with regard to control at the level of reinitiation.