Evolution

Although it remains unproven, group II introns are widely accepted to be the ancestors of spliceosomal introns found in higher eukaryotes, including humans. The idea is supported by a common splicing mechanism, and by structural similarities between group II introns and the snRNA/intron/exon pairings that form in the spliceosome during the splicing reaction.         

            Group II introns are also related to non-LTR retroelements, a prominent class of nuclear retroelements. The best known non-LTR elements are LINE elements, that make up roughly 20% of the human genome. In fact, the RTs of non-LTR elements are fairly closely related phylogenetically to group II introns, and further, the mobility mechanisms of both elements are known as target-primed reverse transcription (TPRT).   Zimmerly et al 2001