A kinetic analysis of aminoacylation of mutant yeast tRNAphe transcripts by its cognate yeast phenylalanyl-tRNA synthetase (FRS) reveals five nucleotides in tRNAPhe as major recognition sites for FRS. The aminoacylation kinetics for two double mutants suggest that each of the five recognition sites contributes independently to kcat/KM. Measured kinetic values for the mutants presented here and those reported previously were then used to calculate the predicted cat/KM. of misacylation for a number of noncognate tRNAs. The predicted cat/KM. values are consistent with values measured by other investigators and thus support the five-nucleotide recognition model. The cat/KM. of misacylation for all known yeast tRNAs has been calculated on the basis of this model, and the specificity of FRS for tRNAPhe in yeast is discussed.
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