Résumé
Multiple interactions with DNA, RNA and transcription factors occur in a transcription cycle. To survey the proximity of some of these factors to the Escherichiacoli RNA polymerase surface, we produced a set of nine monoclonal antibodies (mAbs) against the enzyme. These mAbs, located at different places on the surface of the enzyme, were used in a co-immunopurification assay to investigate interference with the binding of NusA, σ70, GreB and HepA to core RNA polymerase. One of these mAbs turned out to be the first antibody inhibitor of the binding of NusA and σ70; it did not affect GreB and HepA interactions. Its epitope was located on the β′ subunit at the C-terminus of region G. The properties of this mAb reinforce the idea that the mutually exclusive binding of NusA and σ70 to core RNA polymerase is due to, at least partially, overlapping binding sites, rather than allosteric interaction between two distant binding sites. This mAb is also useful to understand the occupancy of σ70, NusA and Gre proteins on core RNA polymerase.