title: Self-splicing group I introns in eukaryotic viruses.
abstract: We report the occurrence of self-splicing group I introns in viruses that infect the eukaryotic green alga Chlorella. The introns contained all the conserved features of primary sequence and secondary structure previously described for the group IB introns. The Chlorella viral introns (approximately 400 nt) self-spliced in vitro, yielding the typical group I intron splicing intermediates and products. Contrasting to eukaryotic nuclear group I introns, all of which are located in the rRNA genes, these introns were inserted in genes encoding proteins. In one case, the exons encoded a protein showing significant homology to the eukaryotic transcription factor SII (TFIIS), which may be important for viral gene expression. In another case, the gene for the open reading frame (ORF) of a 14.2 kDa polypeptide with unknown functions contained the intron. Scattered distribution of these introns among the viral species and their structural similarity to the group I introns of algae and protists indicated horizontal intron transmission. These eukaryotic viral introns offer an opportunity to understand how group I introns reach organisms of different phylogenetic kingdoms.
authors.affiliation: Department of Fermentation Technology, Faculty of Engineering, Hiroshima University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamada
authors.forename: K
authors.initials: K
authors.lastname: Tamura
authors.forename: T
authors.initials: T
authors.lastname: Aimi
authors.forename: P
authors.initials: P
authors.lastname: Songsri
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002708:Chlorella; D004267:DNA Viruses / Q000235:genetics*; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012326:RNA Splicing; D012367:RNA, Viral / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics; D035165:Transcription Factors, General; D035602:Transcriptional Elongation Factors
chemical_list: D012367:RNA, Viral; D014157:Transcription Factors; D035165:Transcription Factors, General; D035602:Transcriptional Elongation Factors; C018648:transcription factor S-II