RNA catalysis: ribozymes, ribosomes, and riboswitches.

The catalytic mechanisms employed by RNA are chemically more diverse than initially suspected. Divalent metal ions, nucleobases, ribosyl hydroxyl groups, and even functional groups on metabolic cofactors all contribute to the various strategies employed by RNA enzymes. This catalytic breadth raises intriguing evolutionary questions about how RNA lost its biological role in some cases, but not in others, and what catalytic roles RNA might still be playing in biology.