RELEASE FACTOR RF3 IN ESCHERICHIA-COLI ACCELERATES THE DISSOCIATION OF RELEASE FACTORS RF1 AND RF2 FROM THE RIBOSOME IN A GTP-DEPENDENT MANNER

Ribosomes complexed with synthetic mRNA and peptidyl-tRNA, ready for p eptide release, were purified by gel filtration and used to study the function of release factor RF3 and guanine nucleotides in the terminat ion of protein synthesis. The peptide-releasing activity of RF1 and RF 2 in limiting concentrations was stimulated by the addition of RF3 and GTP, stimulated, though to a lesser extent, by RF3 and a non-hydrolys able GTP analogue, and inhibited by RF3 and GDP or RF3 without guanine nucleotide. With short incubation times allowing only a single cataly tic cycle of RF1 or RF2, peptide release activity was independent of R F3 and guanine nucleotide. RF3 hydrolysis of GTP to GDP + P-i was depe ndent only on ribosomes and not oh RF1 or RF2. RF3 affected neither th e rate of association of RF1 and RF2 with the ribosome nor the catalyt ic rate of peptide release. A model is proposed which explains how RF3 recycles RF1 and RF2 by displacing the factors from the ribosome afte r the release of peptide.