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Organization of an Activator-Bound RNA Polymerase Holoenzyme
Daniel Bose1,4,Tillmann Pape1,4,Patricia C. Burrows2,Mathieu Rappas1,5,Siva R. Wigneshweraraj3,Martin Buck2andXiaodong Zhang1,,
1 Division of Molecular Biosciences, Centre for Structural Biology, Department of Life Sciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, UK
2 Division of Biology, Department of Life Sciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, UK
3 Division of Investigative Science, Department of Microbiology, Faculty of Medicine, Imperial College London, London SW7 2AZ, UK
Transcription initiation involves the conversion from closed promoter complexes, comprising RNA polymerase (RNAP) and double-stranded promoter DNA, to open complexes, in which the enzyme is able to access the DNA template in a single-stranded form. The complex between bacterial RNAP and its major variant sigma factor σ54 remains as a closed complex until ATP hydrolysis-dependent remodeling by activator proteins occurs. This remodeling facilitates DNA melting and allows the transition to the open complex. Here we present cryoelectron microscopy reconstructions of bacterial RNAP in complex with σ54 alone, and of RNAP-σ54 with an AAA+ activator. Together with photo-crosslinking data that establish the location of promoter DNA within the complexes, we explain why the RNAP-σ54 closed complex is unable to access the DNA template and propose how the structural changes induced by activator binding can initiate conformational changes that ultimately result in formation of the open complex.