title: A large number of nuclear genes in the human parasite blastocystis require mRNA polyadenylation to create functional termination codons.
abstract: Termination codons in mRNA molecules are typically specified directly by the sequence of the corresponding gene. However, in mitochondria of a few eukaryotic groups, some mRNAs contain the termination codon UAA deriving one or both adenosines from transcript polyadenylation. Here, we show that a similar phenomenon occurs for a substantial number of nuclear genes in Blastocystis spp., divergent unicellular eukaryote gut parasites. Our analyses of published genomic data from Blastocystis sp. subtype 7 revealed that polyadenylation-mediated creation of termination codons occurs in approximately 15% of all nuclear genes. As this phenomenon has not been noticed before, the procedure previously employed to annotate the Blastocystis nuclear genome sequence failed to correctly define the structure of the 3'-ends of hundreds of genes. From sequence data we have obtained from the distantly related Blastocystis sp. subtype 1 strain, we show that this phenomenon is widespread within the Blastocystis genus. Polyadenylation in Blastocystis appears to be directed by a conserved GU-rich element located four nucleotides downstream of the polyadenylation site. Thus, the highly precise positioning of the polyadenylation in Blastocystis has allowed reduction of the 3'-untranslated regions to the point that, in many genes, only one or two nucleotides of the termination codon are left.
authors.affiliation: Department of Biology and Ecology, Faculty of Science, University of Ostrava, Czech Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Klimeš
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Eleni
authors.initials: E
authors.lastname: Gentekaki
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, CanadaIntegrated Microbial Biodiversity Program, Canadian Institute for Advanced Research, Halifax, Nova Scotia, Canada.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Roger
authors.affiliation: Department of Biology and Ecology, Faculty of Science, University of Ostrava, Czech Republic marek.elias@osu.cz.
authors.forename: Marek
authors.initials: M
authors.lastname: Eliáš
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D016844:Blastocystis / Q000737:chemistry / Q000235:genetics*; D016776:Blastocystis Infections / Q000469:parasitology*; D018388:Codon, Terminator / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D026723:Polyadenylation; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics*
chemical_list: D018388:Codon, Terminator; D015800:Protozoan Proteins; D012333:RNA, Messenger
keywords: Blastocystis; evolution; gene expression; mRNA processing; polyadenylation; termination codons; translation