<p> Certain aminoacyl-tRNA synthetases prevent potential errors in protein synthesis through deacylation of mischarged tRNAs. The close homologs isoleucyl-tRNA synthetase (IleRS) and valyl-tRNA synthetase (ValRS) deacylate Val-tRNAIle and Thr-tRNAVal, respectively. These reactions strictly require the presence of the cognate tRNA. In the absence of tRNA, the enzymatically generated misactivated adenylates remain in the active site, sequestered from hydrolysis. Upon addition of cognate tRNA the misactivated amino acids are hydrolyzed, regenerating the free tRNA and amino acid, while converting 1 equivalent of ATP to AMP. A prominent mechanism for editing misactivated amino acids is the rapid hydrolysis of transiently mischarged tRNA. This reaction is catalyzed at a second active site on IleRS and ValRS. This site is located within a large insertion (termed CP1) into the canonical class I aminoacyl-tRNA synthetase active-site fold. The CP1 domain as an isolated polypeptide hydrolyzes its cognate mischarged tRNA [<cite idref="PUB00011778"/>].</p> Valyl/Leucyl/Isoleucyl-tRNA synthetase, class Ia, editing domain