Crystal Structure of the Catalytic Core of an RNA-Polymerase Ribozyme

Revealing the RNA World? The RNA World hypothesis posits that at an early step in the appearance of life, RNA acted both as an information storage molecule and as an enzyme—or ribozyme. Such dual functionality would allow for an RNA species that could replicate itself and thus seed the beginning of molecular evolution. The involvement of RNA in a number of fundamental cell biological processes, together with its ability, either naturally or through in vitro evolution, to catalyze a range of chemical reactions, provides some indirect support for this view. Shechner et al. (p. 1271 ) have now determined the structure of an in vitro–evolved RNA ligase ribozyme that catalyses a chemical reaction essentially identical to that of proteins that replicate RNA. The active site of the RNA ligase could be superimposed upon that of the protein enzyme to reveal analogous residues important for the catalytic joining of RNA moieties. These findings will help in the engineering of more effective ribozyme polymerases.