title: Enhanced self-splicing of Physarum polycephalum intron 3 by a second group I intron.
abstract: The third group I intron of Physarum polycephalum is found at the same site in the large subunit rRNA as the well-characterized intron from Tetrahymena thermophila. Formation of alternative structures in the rRNA can inhibit self-splicing of the Tetrahymena intron. We report that splicing of Physarum intron 3 is also influenced by adjacent sequences. In this case, however, splicing is stimulated by the presence of a second group I intron 24 nucleotides downstream. In vitro, intron 3 self-splices 10-25-fold faster in transcripts containing both introns. In vivo, intron 3 is excised from pre-rRNA before intron 2 in the majority of transcripts, as judged by PCR amplification of processing intermediates. This is an unusual example in which self-splicing is enhanced by the juxtaposition of two group I introns. This cooperative effect may be mediated by a conformational change in the rRNA.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park 20742-2021, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Rocheleau
authors.forename: S A
authors.initials: SA
authors.lastname: Woodson
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D017125:Genes, Protozoan; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016839:Physarum polycephalum / Q000235:genetics*; D012322:RNA Precursors / Q000378:metabolism; D016337:RNA, Catalytic / Q000378:metabolism*; D016053:RNA, Protozoan / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D012322:RNA Precursors; D016337:RNA, Catalytic; D016053:RNA, Protozoan; D012335:RNA, Ribosomal; C065096:RNA, ribosomal, 26S