Proofreading of the codon-anticodon interaction on ribosomes.

Abstract
The fidelity of protein synthesis is substantially greater than the specificity of codon-anticodon recognition that would be expected from the known energetics of base-pairing in solution. To test the suggestion that the specificity of recognition may be increased by kinetic proofreading associated with GTP hydrolysis, the interaction of ternary complexes of polypeptide elongation factor Tu, aminoacyl[aa]-tRNA and GTP with poly(U)-programed ribosomes [from Escherichia coli] was studied. With most noncognate ternary complexes, including 2 that pair correctly with the 5'' and 3'' bases of UUU, rejection occurred without GTP hydrolysis, presumably by the reverse of the initial binding reaction. With complexes containing Leu- or Ile-tRNAs, which may pair correctly with the 3'' and middle bases, GTP hydrolysis was stimulated, though the aa-tRNA was not retained on the ribosome. The existence of a GTP-dependent proofreading step in aminoacyl-tRNA recognition on ribosomes is thus demonstrated. The 5'' base of the codon is probably more prone than the middle base to errors that can be corrected by proofreading.