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The elongation cycle of ribosomal protein synthesis begins with the binding of the substrate, aminoacyl-tRNA, to the A site of the ribosome. The reaction is a quite complex process which involves an enzyme, elongation factor Tu (EF-Tu), and GTP. It is the complex of aminoacyl-tRNA with EF-Tu and GTP (“ternary complex”) which rapidly associates with the A site (Miller and Weissbach, 1977; Kaziro, 1978). Subsequently, the recognition of the codon takes place. The formation of the codonanticodon complex provides the signal which triggers the hydrolysis of GTP. The latter enables the dissociation of EF-Tu•GDP from the ribosome which in turn allows the aminoacyl-tRNA to accommodate in the A site such as to be positioned correctly for peptidyl transfer. There is good evidence supporting the view that the complexity of the A-site binding reaction, at least in part, is due to the necessity to optimize speed and accuracy of aminoacyl-tRNA selection by the inclusion of proofreading during the process (Thompson and Dix, 1982; Thompson and Karim, 1982; Ehrenberg and Kurland, 1984; Ruusala et al., 1984). |
