DNA aptamer targets translational editing motif in a tRNA synthetase

Potential errors in translation occur when the wrong amino acid is activated by an aminoacyl tRNA synthetase to form a misactivated aminoacyladenylate. The misactivated amino acid can in the next step be attached to a tRNA that has an anticodon different than the ones corresponding to the amino acid. If the misacylated tRNA donates its amino acid to a growing polypeptide chain, then an error of translation occurs. However, certain tRNA synthetases have an editing activity that corrects errors of misactivation and of misacylation. The relationship between these two error-correcting activities in a synthetase has not been clear. We showed recently that an insertion (known as CP1) into the active site of a class I tRNA synthetases has a deacylase activity that hydrolytically removes mischarged amino acids that are attached to tRNAs. In other work, we showed that a specific DNA aptamer, selected from a random pool, could stimulate hydrolytic breakdown of a misactivated aminoacyladenylate bound to a tRNA synthetase. In this work, we photo-crosslinked the DNA aptamer to the tRNA synthetase. A single crosslinked peptide on the synthetase was identified. This peptide is located within the CP1 insertion, adjacent to residues known to affect the amino acid specificity of the tRNA deacylase activity. These results raise the possibility that the CPI insertion has a role not only in correcting misacylations, but also in the hydrolytic breakdown of misactivated aminoacyladenylates. (C) 1997 Elsevier Science Ltd.