Group II introns are autocatalyic, self-splicing introns (“ribozymes”) that are found in bacteria and the mitochondrial and chloroplast DNAs of some eukaryotes and are evolutionary ancestors of spliceosomal introns and the spliceosome in higher organisms. Thus, studies of group II introns can provide insight into the origin of introns and the evolution of splicing mechanisms in higher organisms. Remarkably, some group II introns are mobile genetic elements, suggesting how introns originated and spread in eukaryotic nuclear genomes. We found that such mobile group II introns encode proteins that are reverse transcriptases (RTs) and can insert site-specifically into new DNA sites by using a novel mechanism (“retrohoming”) in which the intron RNA inserts directly into the DNA site and is reverse transcribed by the intron-encoded protein, yielding an intron cDNA is integrated into the genome by host cell DNA recombination and repair enzymes. In practical applications of this work, we developed mobile group II introns into RNA-guided gene targeting vectors (“targetrons”) and used them as a source of novel RTs with desirable properties for RNA-seq and other biotechnological applications.

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