Catalysis by RNA

Until the discovery of catalytic RNA, the notion that all enzymes are proteins had seemed incontrovertible. Now the existence of RNA enzymes has been confirmed in a variety of contexts. What is known about the chemistry of RNA-catalyzed reactions is reviewed below, with particular attention to the self-splicing rRNA intron of Tetrahymena thermophila and the processing of pre-tRNA molecules by RNase P.