title: Origin and evolution of group I introns in cyanobacterial tRNA genes.
abstract: Many tRNA(Leu)UAA genes from plastids contain a group I intron. An intron is also inserted in the same gene at the same position in cyanobacteria, the bacterial progenitors of plastids, suggesting an ancient bacterial origin for this intron. A group I intron has also been found in the tRNA(fMet) gene of some cyanobacteria but not in plastids, suggesting a more recent origin for this intron. In this study, we investigate the phylogenetic distributions of the two introns among cyanobacteria, from the earliest branching to the more derived species. The phylogenetic distribution of the tRNA(Leu)UAA intron follows the clustering of rRNA sequences, being either absent or present in clades of closely related species, with only one exception in the Pseudanabaena group. Our data support the notion that the tRNA(Leu)UAA intron was inherited by cyanobacteria and plastids through a common ancestor. Conversely, the tRNA(fMet) intron has a sporadic distribution, implying that many gains and losses occurred during cyanobacterial evolution. Interestingly, a phylogenetic tree inferred from intronic sequences clearly separates the different tRNA introns, suggesting that each family has its own evolutionary history.
authors.affiliation: Department of Biological Sciences and Center for Molecular Genetics, University at Albany-SUNY, New York 12222, USA.
authors.forename: B
authors.initials: B
authors.lastname: Paquin
authors.forename: S D
authors.initials: SD
authors.lastname: Kathe
authors.forename: S A
authors.initials: SA
authors.lastname: Nierzwicki-Bauer
authors.forename: D A
authors.initials: DA
authors.lastname: Shub
mesh_terms: D017124:Conserved Sequence; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics*; D019143:Evolution, Molecular; D005798:Genes, Bacterial; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012335:RNA, Ribosomal / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics*; D012356:RNA, Transfer, Leu / Q000235:genetics; D012358:RNA, Transfer, Met / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
chemical_list: D012335:RNA, Ribosomal; D012356:RNA, Transfer, Leu; D012358:RNA, Transfer, Met; C089238:fMet-tRNA(fMet); D012343:RNA, Transfer