Conformational Changes of Escherichia coli σ54-RNA-Polymerase upon Closed–Promoter Complex Formation

RNA polymerase from the mesophile Escherichia coli exists in two forms, the core enzyme and the holoenzyme. Using cryo-electron microscopy and single-particle analysis, we have obtained the structure of the complete RNA polymerase from E. coli containing the σ54 factor within the closed-promoter complex. Comparisons with earlier reconstructions of the core enzyme and the σ54 holoenzyme reveal the behaviour of this major variant RNA polymerase in defined functional states. The binding of DNA leads to significant conformational changes in the enzymeʹs catalytic subunits, apparently a necessity for the initiation of enhancer-dependent promoter-specific transcription.