Localization of a σ70 binding site on the N terminus of the Escherichia coli RNA polymerase β′ subunit

The Escherichia coli genome encodes genes for seven different a subunit species while only having single genes for the alpha, beta, and beta' subunits that make up the RNA polymerase core enzyme. The various sigma factors compete for binding to the core enzyme, upon which they confer promoter; DNA-specific transcription initiation to the polymerase. We have mapped a major interaction site between one of the a species, sigma(70), and beta'. Using far-Western blotting analysis of chemically cleaved and genetically engineered protein fragments, we have identified a N-terminal fragment of beta' (residues 60-309) that could bind sigma(70). We were able to more precisely map the interaction domain to amino acid residues 260-309 of beta' using nickel nitrilotriacetic acid co-immobilization assays.