title: In vivo mobility of a group I twintron in nuclear ribosomal DNA of the myxomycete Didymium iridis.
abstract: DiSSU1 is an optional group I twintron present in the nuclear extrachromosomal ribosomal DNA of the myxomycete Didymium iridis. DiSSU1 appears to be complex both in structure and function. At the RNA level it has a twin-ribozyme organization composed of two group I ribozymes with different functions, separated by an open reading frame. Here, we show that DiSSU1 is mobile when haploid intron-containing and intron-less amoebae are mated. The mobility process is fast, being completed in 5-10 nuclear cycles after mating in the developing zygote and plasmodia. Analyses of progeny from genetic crosses confirm intron mobility. DiSSU1 is the first example of a mobile group I twintron. The intron-encoded protein was expressed in Escherichia coli and found to be an endonuclease, I-DirI, that cleaves an intron-less ribosomal DNA allele at the intron-insertion site, and is probably involved in intron homing. The endonuclease I-DirI seems to be a rare example of a protein that is expressed from a ribozyme-processed RNA polymerase I transcript in vivo.
authors.affiliation: Department of Molecular Cell Biology, Institute of Medical Biology, University of Tromsø, Norway. steinarj@fagmed.uit.no
authors.forename: S
authors.initials: S
authors.lastname: Johansen
authors.forename: M
authors.initials: M
authors.lastname: Elde
authors.forename: A
authors.initials: A
authors.lastname: Vader
authors.forename: P
authors.initials: P
authors.lastname: Haugen
authors.forename: K
authors.initials: K
authors.lastname: Haugli
authors.forename: F
authors.initials: F
authors.lastname: Haugli
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004251:DNA Transposable Elements; D004271:DNA, Fungal / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics*; D004720:Endonucleases / Q000235:genetics; D005800:Genes, Fungal; D007438:Introns; D008969:Molecular Sequence Data; D009235:Myxomycetes / Q000235:genetics*; D009694:Nucleic Acid Precursors / Q000235:genetics; D011110:Polymorphism, Genetic; D012323:RNA Processing, Post-Transcriptional; D016337:RNA, Catalytic; D012331:RNA, Fungal / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D004271:DNA, Fungal; D004275:DNA, Ribosomal; D009694:Nucleic Acid Precursors; D016337:RNA, Catalytic; D012331:RNA, Fungal; D004720:Endonucleases