Structural Organization of Bacterial RNA Polymerase Holoenzyme and the RNA Polymerase-Promoter Open Complex

We have used systematic fluorescence resonance energy transfer and distance-constrained docking to define the three-dimensional structures of bacterial RNA polymerase holoenzyme and the bacterial RNA polymerase-promoter open complex in solution. The structures provide a framework for understanding σ 70-(RNA polymerase core), σ 70-DNA, and σ 70-RNA interactions. The positions of σ 70 regions 1.2, 2, 3, and 4 are similar in holoenzyme and open complex. In contrast, the position of σ 70 region 1.1 differs dramatically in holoenzyme and open complex. In holoenzyme, region 1.1 is located within the active-center cleft, apparently serving as a “molecular mimic” of DNA, but, in open complex, region 1.1 is located outside the active center cleft. The approach described here should be applicable to the analysis of other nanometer-scale complexes.