Structural Dynamics of the Translating Ribosome

Abstract

The process of translation (elongation) on the ribosome is composed of repeating cycles, each consisting of three successive steps: aminoacyl-tRNA binding, transpeptidation, and translocation. The question arises: Is any step of the elongation cycle accompanied by mechanical alterations of the ribosomal particle? This question is practically appropriate in considering the translocation step as it includes intraribosomal displacements of a template and the products of the transpeptidation reaction, e.g., the release of deacylated tRNA, the transport of peptidyl-tRNA from one site to the other, and the shift of the template polynucleotide by one codon. The possibility of “an alternate contraction and expansion of the ribosome” (“a pulsating ribosome contraction”) in the elongation cycle was first suggested by Lipmann and co-workers (Conway and Lipmann, 1964; Nishizuka and Lipmann, 1966). This question was posed, most clearly in 1968 when the idea of a type of moving apart (unlocking) of the two coupled ribosomal subunits as a plausible driving mechanism for translocation was proposed (Spirin, 1968).