title: Recurrent invasion of mitochondrial group II introns in specimens of Pylaiella littoralis (brown alga), collected worldwide.
abstract: The mitochondrial genome of a filamentous brown alga Pylaiella littoralis (strain CCMP 1907) has been reported to contain four group IIB introns in the LSU rRNA gene and three group IIA introns in the cox1 gene. We found extreme variability in the number of group II introns for these two genes by analyzing eight P. littoralis specimens collected at worldwide habitats. The first intron of the LSU rRNA gene from a specimen collected in France and the fourth intron from a specimen harvested in Japan exhibited an exceptionally long evolutionary distance when compared with the cognate introns found in P. littoralis specimens. Moreover, these introns harbored an intact or nearly intact tripartite ORF, suggesting they are the result of a recent invasion of cognate introns. Based on the fact that many of the target sites were intronless, we propose that opportunity of intron infection is the bottleneck step of the group II intron cycle which consists of invasion, degeneration, and complete loss from the target site.
authors.affiliation: Department of Biology, Osaka Kyoiku University, Kashiwara, Osaka 582-8582, Japan. ikuta@cc.osaka-kyoiku.ac.jp
authors.forename: Kyosuke
authors.initials: K
authors.lastname: Ikuta
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawai
authors.forename: Dieter G
authors.initials: DG
authors.lastname: Müller
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ohama
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004275:DNA, Ribosomal / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics; D019143:Evolution, Molecular; D050259:Genes, Mitochondrial / Q000235:genetics*; D005843:Geography; D007438:Introns / Q000235:genetics*; D008928:Mitochondria / Q000201:enzymology / Q000235:genetics*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D000459:Phaeophyceae / Q000166:cytology / Q000201:enzymology / Q000235:genetics*; D010802:Phylogeny; D011110:Polymorphism, Genetic; D016415:Sequence Alignment
chemical_list: D004275:DNA, Ribosomal; D024101:Mitochondrial Proteins; D003576:Electron Transport Complex IV