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Updated: Apr 27, 2026
Analysis of Termination of Transcription Using BrUTP-strand-specific Transcription Run-on TRO Approach
Published on: March 12, 2017
A large number of nuclear genes in the human parasite blastocystis require mRNA polyadenylation to create functional
Vladimír Klimeš1, Eleni Gentekaki2, Andrew J Roger3
1Department of Biology and Ecology, Faculty of Science, University of Ostrava, Czech Republic.
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.
Insights
In Blastocystis parasites, gene sequences don't always signal the end of mRNA. Polyadenylation, a process adding nucleotides, creates termination codons in about 15% of nuclear genes, a novel finding.
Area of Science:
- Molecular Biology
- Eukaryotic Genetics
- Parasitology
Background:
- Termination codons (UAA) in mRNA typically derive from gene sequences.
- Mitochondrial mRNAs in some eukaryotes use polyadenylation to form termination codons.
- This study investigates a similar phenomenon in the nuclear genes of Blastocystis spp.
Discussion:
- Polyadenylation-mediated termination codon creation occurs in ~15% of Blastocystis sp. subtype 7 nuclear genes.
- This finding corrects previous genome annotation errors regarding 3'-end gene structures.
- The phenomenon is widespread across different Blastocystis subtypes, indicating a conserved mechanism.
Key Insights:
- Blastocystis spp. utilize polyadenylation to generate termination codons in a significant portion of nuclear genes.
- A conserved GU-rich element downstream of the polyadenylation site directs this process.
- This mechanism allows for highly reduced 3'-untranslated regions in many Blastocystis genes.
Outlook:
- Further research into the regulatory mechanisms and evolutionary implications of polyadenylation-mediated termination.
- Potential impact on gene expression regulation and protein synthesis in Blastocystis.
- Implications for comparative genomics and understanding gene annotation in related organisms.
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