DNA APTAMER TARGETS TRANSLATIONAL EDITING MOTIF IN A TRANSFER-RNA SYNTHETASE

Potential errors in translation occur when the wrong amino acid is act ivated by an aminoacyl tRNA synthetase to form a misactivated aminoacy ladenylate. The misactivated amino acid can in the next step be attach ed to a tRNA that has an anticodon different than the ones correspondi ng to the amino acid. If the misacylated tRNA donates its amino acid t o a growing polypeptide chain, then an error of translation occurs. Ho wever, 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 cl ear. We showed recently that an insertion (known as CP1) into the acti ve site of a class I tRNA synthetases has a deacylase activity that hy drolytically 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 crosslink ed peptide on the synthetase was identified. This peptide is located w ithin the CP1 insertion, adjacent to residues known to affect the amin o acid specificity of the tRNA deacylase activity. These results raise the possibility that the CPI insertion has a role not only in correct ing misacylations, but also in the hydrolytic breakdown of misactivate d aminoacyladenylates. (C) 1997 Elsevier Science Ltd.