A novel bacterial transcription cycle involving σ54

Abstract

σ54 is the promoter recognition subunit of the form of bacterial RNA polymerase that transcribes from promoters with enhancer elements. DNase footprinting experiments show that σ54 is attached selectively to the template strand, which must be single-stranded for transcription initiation, σ54 remains bound at the promoter after core polymerase begins elongation, in contrast to the well-established σ70-holoenzyme transcription cycle. Permanganate footprinting experiments show that the bound σ54 and the elongating core RNA polymerase downstream of it are each associated with a single-stranded DNA region. Template commitment assays show that the promoter-bound σ54 must be reconfigured before reinitiation of transcription can occur. This unexpected pathway raises interesting possibilities for transcriptional regulation, especially with regard to control at the level of reinitiation.