Novel roles for classical factors at the interface between translation termination and initiation

The pathway of bacterial ribosome recycling following translation terminati on has remained obscure, Here, we elucidate two essential steps and describ e the roles played by the three translation factors EF-G, RRF, and IF3. Rel ease factor RF3 is known to catalyze the dissociation of RF1 or RF2 from ri bosomes after polypeptide release. We show that the next step is dissociati on of 50S subunits from the 70S posttermination complex and that it is cata lyzed by RRF and EF-G and requires GTP hydrolysis. Removal of deacylated tR NA from the resulting 30S:mRNA:tRNA posttermination complex is then necessa ry to permit rapid 30S subunit recycling. We show that this step requires i nitiation factor IF3, whose role was previously thought to be restricted to promoting specific 30S initiation complex formation from free 30S subunits .