Cyanobacterial tRNA(Leu)(UAA) group I introns have polyphyletic origin

Self-splicing group I introns in tRNA anticodon loops have been found in diverse groups of bacteria (alpha, beta purple bacteria and cyanobacteria). In particular, the cyanobacterial tRNA(Leu)(UAA) group I introns have attracted considerable attention because of their presumed ancient origin and immobility. In this work, however, we identified tRNA(Leu)(UAA) group I introns in six out of 16 closely related isolated belonging to the cyanobacterial genus Microcystis. Interestingly, these introns are more closely related to the group I introns identified in the alpha and beta purple bacteria (located in tRNA(Arg)(CCU) and tRNA(Ile)(CAU), respectively) than to other cyanobacterial introns. Our sequence comparison and phyletic reconstruction suggest lateral transfer of the intron (possibly trough mobility), and a polyphyletic origin of cyanobacterial tRNA(Leu)(UAA) group I introns.