Group II intron architecture and its implications for the development of eukaryotic splicing systems

Group II introns are self‐splicing RNA molecules that have played an important role in the evolution of terrestrial genome organization. After splicing, free group II introns are liberated into the cell, where they behave as mobile genetic elements that insert themselves into new RNA or DNA sites. As a result of this behavior, the introns have spread throughout bacteria and eukaryotic lineages, diversifying organisms through the insertion of new introns and by evolving into new types of splicing machinery. The eukaryotic spliceosome is believed to have evolved from an ancestral group II intron that was absorbed during an early endosymbiont event. The functional relationship between group II introns and the spliceosome has long been supported by similarities in splicing mechanism and conserved RNA secondary structures. Recent crystallographic studies of group II introns have provided a high resolution view of active‐site organization, resulting in additional evidence that group II‐like components lie within the catalytic heart of the eukaryotic spliceosome.