Polypeptides containing highly conserved regions of transcription initiation factor σ70 exhibit specificity of binding to promoter DNA

Abstract

The σ 70 subunit of E. coli RNA polymerase is required for sequence-specific recognition of promoter DNA. Genetic studies and sequence analysis have indicated that σ 70 contains two specific DNA-binding domains that recognize the two conserved portions of the prokaryotic promoter. However, intact σ 70 does not bind to DNA. Using C-terminal and internal polypeptides of σ 70, carrying one or both putative DNA-binding domains, we demonstrate that σ 70 does contain two DNA-binding domains, but that N-terminal sequences inhibit the ability of intact σ 70 to bind to DNA. Thus, we propose that σ 70 is a sequence-specific DNA-binding protein that normally functions through an allosteric interaction with the core subunits of RNA polymerase.