CONFORMATIONAL-CHANGES IN THE TRANSCRIPTION COMPLEX OF RNA-POLYMERASEAND DNA

Using paramagnetic and fluorescing labels, we have shown that E. colt RNA polymerase (E sigma 70) bound with T2 phage DNA undergoes several specific conformational transitions, which optimize the active site st ructure at different stages of RNA synthesis. DNA is a conformational cofactor of RNA polymerase and induces in it specific changes associat ed with formation of transcriptionally competent complexes. Use of a b ifunctional fluorescence label, fluorescein dimercuriacetate, allowed detection of protein regions with relatively independent conformationa l mobility. The functional significance of the conformational mobility of local regions in RNA polymerase is discussed.