In vivo mobility of a group I twintron in nuclear ribosomal DNA of the myxomycete Didymium iridis.
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.
Johansen
S
S
Department of Molecular Cell Biology, Institute of Medical Biology, University of Tromsø, Norway. steinarj@fagmed.uit.no
Elde
M
M
Vader
A
A
Haugen
P
P
Haugli
K
K
Haugli
F
F
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
D004251:DNA Transposable Elements; D004271:DNA, Fungal; D004275:DNA, Ribosomal; D009694:Nucleic Acid Precursors; D016337:RNA, Catalytic; D012331:RNA, Fungal; D004720:Endonucleases