Transposition and exon shuffling by group II intron RNA molecules in pieces

In the realms of RNA, transposable elements created by self-inserting intro ns recombine novel combinations of exon sequences in the background of repl icating molecules. Although intermolecular MA recombination is a wide-sprea d phenomenon reported for a variety of RNA-containing viruses, direct evide nce to support the theory that modern splicing systems, together with the e xon-intron structure, have evolved from the ability of RNA to recombine, is lacking. Here, we used an in vitro deletion-complementation assay to demon strate trans-activation of forward and reverse self-splicing of a fragmente d derivative of the group II intron bI1 from yeast mitochondria. We provide direct evidence for the functional interchangeability of analogous but non -identical domain 1 RNA molecules of group II introns that result in trans- activation of intron transposition and RNA-based exon shuffling. The data e xtend theories on intron evolution and raise the intriguing possibility tha t naturally fragmented group III and spliceosomal introns themselves can cr eate transposons, permitting rapid evolution of protein-coding sequences by splicing reactions. (C) 2000 Academic Press.