The RNA origin of transfer RNA aminoacylation and beyond.

Aminoacylation of tRNA is an essential event in the translation system. Although in the modern system protein enzymes play the sole role in tRNA aminoacylation, in the primitive translation system RNA molecules could have catalysed aminoacylation onto tRNA or tRNA-like molecules. Even though such RNA enzymes so far are not identified from known organisms, in vitro selection has generated such RNA catalysts from a pool of random RNA sequences. Among them, a set of RNA sequences, referred to as flexizymes (Fxs), discovered in our laboratory are able to charge amino acids onto tRNAs. Significantly, Fxs allow us to charge a wide variety of amino acids, including those that are non-proteinogenic, onto tRNAs bearing any desired anticodons, and thus enable us to reprogramme the genetic code at our will. This article summarizes the evolutionary history of Fxs and also the most recent advances in manipulating a translation system by integration with Fxs.