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 cyanoba cteria). In particular, the cyanobacterial tRNA(Leu)(UAA) group I intr ons have attracted considerable attention because of their presumed an cient origin and immobility. In this work, however, we identified tRNA (Leu)(UAA) group I introns in six out of 16 closely related isolates b elonging 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 tRN A(Ile)(CAU), respectively) than to other cyanobacterial introns. Our s equence comparison and phyletic reconstruction suggest lateral transfe r of the intron (possibly trough mobility), and a polyphyletic origin of cyanobacterial tRNA(Leu)(UAA) group I introns.