Molecular biology. Running the red light

Allosteric binding of nucleoside triphosphates to RNA polymerase regulates transcription elongation

The regulation of transcription elongation and termination appears to be governed by the ability of RNA polymerase elongation complexes to adopt multiple conformational states; however, the factors controlling the distribution between these states remain elusive. We used transient-state kinetics to investigate the incorporation of single nucleotides. We demonstrate that E. coli RNA polymerase contains an allosteric binding site in addition to the catalytic site. Binding of the templated nucleoside triphosphate (NTP), but not nontemplated NTPs, to this site increases the rate of nucleotide incorporation. The data suggest that RNA polymerase can exist in a state that catalyzes synthesis slowly (unactivated) and one that catalyzes synthesis rapidly (activated), with the transition from the slow to the fast state being induced by binding of the templated NTP to the allosteric site.