Flexizymes: their evolutionary history and the origin of catalytic function.

Transfer RNA (tRNA) is an essential component of the cell’s translation apparatus. These RNA strands contain the anticodon for a given amino acid, and when “charged” with that amino acid are termed aminoacyl-tRNA. 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, our group attempted in vitro selection of artificial ARS-like ribozymes, successfully uncovering a functional ribozyme (r24) from an RNA pool of random sequences attached to the 5′-leader region of tRNA. This ribozyme preferentially charges aromatic amino acids (such as phenylalanine) activated with cyanomethyl ester (CME) onto specific kinds of tRNA.During the course of our studies, we became interested in developing a v...