Transfer RNA (tRNA) is an essential component of the cell's translation apparatus. Aminoacylation, which occurs exclusively at one of the 3'-terminal hydroxyl groups of tRNA, is catalyzed by a family of enzymes called aminoacyl-tRNA synthetases (ARSs). In a primitive translation system, before the advent of sophisticated protein-based enzymes, this chemical event could conceivably have been catalyzed solely by RNA enzymes. Given the evolutionary implications, Suga and co-workers attempted in vitro selection of artificial ARS-like ribozymes, successfully uncovering a functional ribozyme (r24) capable of charging activated aromatic amino acids onto specific kinds of tRNA.
Morimoto J, Hayashi Y, Iwasaki K, Suga H.
Flexizymes: their evolutionary history and the origin of catalytic function.
Acc Chem Res. 2011 Dec 20;44(12):1359-68.