Group I and group II introns

Group I and group II introns are two types of RNA enzymes, ribozymes, that catalyze their own splicing by different mechanisms. In this review, we summarize current information about the structures of-group I and group II introns, their RNA-catalyzed reactions, the facilitation of RNA-catalyzed splicing by protein factors, and the ability of the introns to function as mobile elements. The RNA-based enzymatic reactions and intron mobility provide a framework for considering the role of primordial catalytic RNAs in evolution and the origin of introns in higher organisms.