Lack of Correlation between Affinity of the tRNA for the Aminoacyl-tRNA Synthetase and Aminoacylation Capacity as Studied with Modified tRNAPhe

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Abstract
The interactions of several modified brewer''s yeast tRNAPhe [tRNAPhe lacking 7-methylguanine; a fragment comprising about 3/4 of the whole molecule: tRNAPhe (18-76); tRNAPhe (18-76) lacking 7-methylguanine] with yeast phenylalanyl-tRNA synthetase were studied. Upon excision of the 5''-quarter of the tRNAPhe molecule, the residual fragment still tightly binds to the synthetase, but can no longer be aminoacylated. Surprisingly, upon removal of the 7-methylguanine base at position 46 in this fragment, although the affinity drops by a factor 10, a significant aminoacylation is restored. These results are discussed in terms of molecular flexibility and a model is proposed for tRNA-enzyme interaction, involving multisite recognition.