Codon-anticodon interaction at the ribosomal P site improves the accuracy of the decoding process.

The competing incorporation of [14C]Phe (cognate) and [3H]Leu (miscognate) into polypeptide material was measured. Kinetic analysis revealed that at the very beginning of protein synthesis the error fraction was 3 to 10 times larger than the "system-inherent" error, which is the error fraction found on the synthesized proteins. However, if a cognate tRNA, namely either deacylated tRNAPhe or AcPhe-tRNAPhe were prebound to the ribosomal P site, no enhanced error fraction was observed at the beginning. Furthermore, the initial rate of protein synthesis was increased by a factor of 10 to 50, regardless as to whether the ribosomes were precharged with tRNAPhe or AcPhe-tRNAPhe. In contrast, preincubation of ribosomes with non-cognate tRNA such as deacylated tRNALys had no effect. We conclude that codon-anticodon interaction at the P site facilitates the precise exposure of the adjacent codon at the ribosomal A site, thus contributing to the velocity and precision of the decoding process.