Substrate-binding ability of Escherichia coli ribonucleic acid polymerase in relation to its protein composition

Interaction between Escherichia coli RNA polymerase and its substrates, the nucleoside triphosphates, was studied by gel-filtration and dialysis-rate-measurement techniques. 2. The holoenzyme bound variable amounts of ATP and GTP. There was no correlation between substrate-binding ability and enzyme activity of different enzyme preparations. 3. The core enzyme bound a maximum of 0.1 mol of ATP/mol of enzyme. The dissociation constant of this interaction was of the order of 1 × 10(-5)M. The core enzyme did not bind GTP. 4. A protein of mol.wt. 60000, which was eluted in the first fraction during phosphocellulose column chromatography of the holoenzyme, bound appreciable amounts of ATP. The dissociation constant of this interaction was of the order of 3 × 10(-5)-5 × 10(-6)M. 5. Evidence presented shows that this protein, and not the sigma factor, is responsible for the observed variation in the ATP-binding ability of the holoenzyme.