Proofreading by aminoacyl-tRNA synthetases

Proofreading can occur at two stages: 1. By hydrolysis of the ester bond of an “incorrect” aminoacyl-AMP intermediate triggered by the binding of the cognate tRNA, 2. Hydrolysis of the ester bond of a “miss-matched” aminoacyl-tRNA. Most aminoacyl-tRNA synthetases possess editing (hydrolytic) sites in addition to the acylation site. Usually, the acylation site rejects an amino acid larger than the cognate aa, due to insufficient room. The editing site hydrolyses aminoacyltRNAs which are smaller than the cognate aa.