Fidelity of Aminoacyl-tRNA Selection on the Ribosome: Kinetic and Structural Mechanisms

The ribosome discriminates between correct and incorrect aminoacyl-tRNAs (aa-tRNAs), or their complexes with elongation factor Tu (EF-Tu) and GTP, according to the match between anticodon and mRNA codon in the A site. Selection takes place at two stages, prior to GTP hydrolysis (initial selection) and after GTP hydrolysis but before peptide bond formation (proofreading). In part, discrimination results from different rejection rates that are due to different stabilities of the respective codon-anticodon complexes. An important additional contribution is provided by induced fit, in that only correct codon recognition leads to acceleration of rate-limiting rearrangements that precede chemical steps. Recent elucidation of ribosome structures and mutational analyses suggest which residues of the decoding center may be involved in signaling formation of the correct codon-anticodon duplex to the functional centers of the ribosome. In utilizing induced fit for substrate discrimination, the ribosome resembles other nucleic acid–programmed polymerases.