Two decades of RNA catalysis.

Twenty years have passed since the initial discovery of catalytic RNA. Although initial discoveries of ribozymes (RNA enzymes) involved phosphoryl transfer reactions on RNA substrates, our knowledge of the biological repertoire of these enzymes was expanded recently as a result of new evidence suggesting that the RNA component of the ribosome catalyzes peptide bond formation. Ribozymes have posed novel challenges for mechanistic studies, but recent investigations have yielded increasing support for chemical mechanisms involving precisely positioned nucleic acid bases with environmentally perturbed pKa values and metal ions. A continuing challenge for RNA enzymologists is the separation of the structural and chemical effects in interpreting experimental results, a challenge that will be overcome as the intriguing fields of RNA enzymology and structural biology continue to expand.