RNA aminoacylation mediated by sequential action of two ribozymes and a nonactivated amino acid.

In the transition from the RNA world to the modern DNA/protein world, RNA-catalyzed aminoacylation might have been a key step towards early translation. A number of ribozymes capable of aminoacylating their own 3' termini have been developed by in vitro selection. However, all of those catalysts require a previously activated amino acid-typically an aminoacyl-AMP-as substrate. Here we present two ribozymes connected by intermolecular base pairing and carrying out the two steps of aminoacylation: ribozyme 1 loads nonactivated phenylalanine onto its phosphorylated 5' terminus, thereby forming a high-energy mixed anhydride. Thereafter, a complex of ribozymes 1 and 2 is formed by intermolecular base pairing, and the "activated" phenylalanine is transferred from the 5' terminus of ribozyme 1 to the 3' terminus of ribozyme 2. This kind of simple RNA aminoacylase complex was engineered from previously selected ribozymes possessing the two required activities. RNA aminoacylation with a nonactivated amino acid as described here is advantageous to RNA world scenarios because initial amino acid activation by an additional reagent (in most cases, ATP) and an additional ribozyme would not be necessary.