Functions of elongation factor G in translocation and ribosome recycling

Abstract

Among the translation factors that assist the ribosome in synthesizing proteins, elongation factor G (EF-G) is the only one that functions in two different phases of protein synthesis, i. e. in the translocation step of the elongation phase and in ribosome disassembly following termination. During translocation two tRNAs move by large distances from one site of the ribosome to the next, adjacent site, with the coupled movement of mRNA by one codon. The process is promoted by EF-G and GTP hydrolysis to proceed at the velocity required for rapid protein synthesis in the cell. During ribosome recycling the ribosomal post-termination complex is dissociated into subunits; the reaction is brought about by EF-G together with the ribosome recycling factor (RRF) and requires GTP hydrolysis. Fundamental questions in understanding EF-G function are: (i) How does EF-G accelerate the movement of tRNAs together with the mRNA on the ribosome; (ii) how does EF-G cooperate with RRF to dissociate the ribosomes; and (iii) how are GTP hydrolysis and Pi release coupled to forward movement and ribosome disassembly? The aim of this review is to summarize the recent insights into the molecular mechanism of translocation and ribosome recycling and the role of EF-G in the two reactions. Detailed accounts focusing on different aspects of translocation can also be found in several recent reviews (Shoji et al., 2009; Dunkle and Cate, 2010; Frank and Gonzalez, 2010).