Specific binding of the transcription factor sigma-54 to promoter DNA.
A central event in transcription is the assembly on DNA of specific complexes near the initiation sites for RNA synthesis. Activation of transcription by one class of enhancer-binding proteins requires an RNA polymerase holoenzyme containing the specialized transcription factor, sigma-54 (sigma 54). We report here that sigma 54 alone specifically binds to promoter DNA and is responsible for many of the close contacts between RNA polymerase holoenzyme and promoter DNA, a property proposed for the major sigma 70 protein family. Binding of sigma 54 to promoter DNA is not equivalent to that of holoenzyme suggesting that there is a constraint on sigma 54 conformation when bound with core RNA polymerase. Footprints indicate sigma 54 is at the leading edge of DNA-bound holoenzyme. Like the holoenzyme, sigma 54-binding to promoter DNA does not result in DNA strand separation. Instead the specific DNA-binding activity of sigma 54 assists assembly of a closed promoter complex. This complex can be isomerized to the open (DNA melted) complex by activator protein, but promoter-bound sigma 54 alone cannot be induced to melt DNA. The pathway leading to productive transcription is similar to that proposed for eukaryotic RNA polymerase II systems.
Buck
M
M
AFRC Nitrogen Fixation Laboratory, University of Sussex, Brighton, UK.
Cannon
W
W
D001483:Base Sequence; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007711:Klebsiella pneumoniae / Q000235:genetics; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012808:Sigma Factor / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000235:genetics
D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012808:Sigma Factor; D012321:DNA-Directed RNA Polymerases