title: Site-specific reverse splicing of a HEG-containing group I intron in ribosomal RNA.
abstract: The wide, but scattered distribution of group I introns in nature is a result of two processes; the vertical inheritance of introns with or without losses, and the occasional transfer of introns across species barriers. Reversal of the group I intron self-splicing reaction, termed reverse splicing, coupled with reverse transcription and genomic integration potentially mediate an RNA-based intron mobility pathway. Compared to the well characterized endonuclease-mediated intron homing, reverse splicing is less specific and represents a likely explanation for many intron transpositions into new genomic sites. However, the frequency and general role of an RNA-based mobility pathway in the spread of natural group I introns is still unclear. We have used the twin-ribozyme intron (Dir.S956-1) from the myxomycete Didymium iridis to test how a mobile group I intron containing a homing endonuclease gene (HEG) selects between potential insertion sites in the small subunit (SSU) rRNA in vitro, in Escherichia coli and in yeast. Surprisingly, the results show a site-specific RNA-based targeting of Dir.S956-1 into its natural (S956) SSU rRNA site. Our results suggest that reverse splicing, in addition to the established endonuclease-mediated homing mechanism, potentially accounts for group I intron spread into the homologous sites of different strains and species.
authors.affiliation: Department of Molecular Biotechnology, Institute of Medical Biology, University of Tromsø N-9037 Tromsø, Norway.
authors.forename: Asa B
authors.initials: AB
authors.lastname: Birgisdottir
authors.forename: Steinar
authors.initials: S
authors.lastname: Johansen
mesh_terms: D000818:Animals; D001483:Base Sequence; D004720:Endonucleases / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D020459:Genes, rRNA; D007438:Introns; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009235:Myxomycetes / Q000235:genetics; D009690:Nucleic Acid Conformation; D012313:RNA / Q000378:metabolism; D012326:RNA Splicing; D016337:RNA, Catalytic / Q000235:genetics* / Q000378:metabolism; D000079962:RNA, Circular; D012335:RNA, Ribosomal / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics
chemical_list: D016337:RNA, Catalytic; D000079962:RNA, Circular; D012335:RNA, Ribosomal; D012313:RNA; D004720:Endonucleases