Key result
Misacylated tRNAs dissociate from the ribosomal A site at similar rates to correctly acylated tRNAs.
The ribosome does not display specificity for different amino acids and tRNA bodies when intact aa-tRNAs are used, or the specificity is masked by a conformational change upon release.
In vitro ribosomal A-site data leave open whether aa-tRNA specificity shapes translation fidelity in cells.
To test whether the ribosome displays specificity for the esterified amino acid and the tRNA body of an aminoacyl-tRNA (aa-tRNA), the stabilities of 4 correctly acylated and 12 misacylated tRNAs in the ribosomal A site were determined. By introducing the GAC (valine) anticodon into each tRNA, a constant anticodon.codon interaction was maintained, thus removing concern that different anticodon.codon strengths might affect the binding of the different aa-tRNAs to the A site. Surprisingly, all 16 aa-tRNAs displayed similar dissociation rate constants from the A site. These results suggest that either the ribosome is not specific for different amino acids and tRNA bodies when intact aa-tRNAs are used or the specificity for the amino acid side chain and tRNA body is masked by a conformational change upon aa-tRNA release.
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Dale et al. (2005) studied this question. Misacylated tRNAs vs. Correctly acylated tRNAs was evaluated on Dissociation rate constants from the ribosomal A site. Both correctly acylated and misacylated tRNAs displayed similar dissociation rate constants from the ribosomal A site, suggesting a lack of specificity for different amino acids and tRNA bodies.
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