title: Complex group-I introns in nuclear SSU rDNA of red and green algae: evidence of homing-endonuclease pseudogenes in the Bangiophyceae.
abstract: The green alga Scenedesmus pupukensis and the red alga Porphyra spiralis contain large group-IC1 introns in their nuclear small subunit ribosomal RNA genes due to the presence of open reading frames at the 5' end of the introns. The putative 555 amino-acid Scenedesmus-encoded protein harbors a sequence motif resembling the bacterial S9 ribosomal proteins. The Porphyra intron self-splices in vitro, and generates both ligated exons and a full-length intron RNA circle. The Porphyra intron has an unusual structural organization by encoding a potential 149 amino-acid homing-endonuclease-like protein on the complementary strand. A comparison between related group-I introns in the Bangiophyceae revealed homing-endonuclease-like pseudogenes due to frame-shifts and deletions in Porphyra and Bangia. The Scenedesmus and Porphyra introns provide new insights into the evolution and possible novel functions of nuclear group-I intron proteins.
authors.affiliation: Department of Molecular Cell Biology, University of Tromsø, Norway.
authors.forename: P
authors.initials: P
authors.lastname: Haugen
authors.forename: V A
authors.initials: VA
authors.lastname: Huss
authors.forename: H
authors.initials: H
authors.lastname: Nielsen
authors.forename: S
authors.initials: S
authors.lastname: Johansen
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D002467:Cell Nucleus / Q000235:genetics; D000460:Chlorophyta / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D004720:Endonucleases / Q000235:genetics*; D007438:Introns; D008969:Molecular Sequence Data; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D011544:Pseudogenes; D012326:RNA Splicing; D016337:RNA, Catalytic / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics; D000461:Rhodophyta / Q000235:genetics*; D017421:Sequence Analysis / Q000379:methods; D017386:Sequence Homology, Amino Acid
chemical_list: D004275:DNA, Ribosomal; D011506:Proteins; D016337:RNA, Catalytic; D012335:RNA, Ribosomal; D004720:Endonucleases