Internal Guide Sequence and Reaction Specificity of Group I Self-splicing Introns

The existence of RNA catalysis in present day biochemistry was demonstrated first and incontrovertibly by the discovery that accurate splicing of the large rRNA precursor of Tetrahymena thermophila occurred in the absence of protein (Cech et al. 1981; Kruger et al. 1982). The intron excised during this self-splicing reaction is a member of a widespread class of introns known as group I introns. This class of introns is common in mitochondrial genomes of fungi, being transcribed into both rRNA and mRNA precursors, and is also found in nuclear genomes of protozoa, in chloroplast genomes of plants, and in bacteriophage. All group I introns are RNA catalysts in various stages of dependence on nuclear or organellar (“maturases”) proteins. The Tetrahymena pre-rRNA (Tet) intron remains the best-studied RNA catalyst, and group I introns may prove to have been the prototypes of all other classes of introns (except those near tRNA anticodons). Their...