Group II intron RNA catalysis of progressive nucleotide insertion: a model for RNA editing

The self-splicing bl1 intron lariat from mitochondria of Saccharomyces cerevisiae catalyzed the insertion of nucleotidyl monomers derived from the 3' end of a donor RNA into an acceptor RNA in a 3' to 5' direction in vitro. In this catalyzed reaction, the site specificity provided by intermolecular base pair interactions, the formation of chimeric intermediates, the polarity of the nucleotidyl insertion, and its reversibility all resemble such properties in previously proposed models of RNA editing in kinetoplastid mitochondria. These results suggest that RNA editing occurs by way of a concerted, two-step transesterification mechanism and that RNA splicing and RNA editing might be prebiotically related mechanisms; possibly, both evolved from a primordial demand for self-replication.