Bacterial Origin of a Chloroplast Intron: Conserved Self-Splicing Group I Introns in Cyanobacteria

A self-splicing group I intron has been found in the gene for a leucine transfer RNA in two species of Anabaena, a filamentous nitrogen-fixing cyanobacterium. The intron is similar to one that is found at the identical position in the same transfer RNA gene of chloroplasts of land plants. Because cyanobacteria were the progenitors of chloroplasts, it is likely that group I introns predated the endosymbiotic association of these eubacteria with eukaryotic cells.