The self-splicing RNAs known as group I introns exist in many organisms, but their distribution is difficult to explain. We hypothesize that group I introns have been transferred between a parasite and its host. We describe here the discovery of a common group I intron sequence between a plant-parasitic fungus, Protomyces inouyei, and its host, Youngia japonica. It strongly supports our theory ...

Group I and group II introns are unrelated classes of introns that each encode proteins that facilitate intron splicing and intron mobility. Here we describe a new subfamily of nine introns in fungi that are group II introns but encode LAGLIDADG ORFs typical of group I introns. The introns have fairly standard group IIB1 RNA structures and are inserted into three different sites in SSU and LSU ...