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Gene linkage and steady state RNAs suggest trans-splicing may be associated with a polycistronic transcript in
1Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA. rdavis@murray.fordham.edu
Abstract:
Spliced leader (SL) trans-splicing generates the 5' end of mature mRNAs through the addition of a small exon to pre-mRNAs in some flagellates (kinetoplastida and euglenoids) and metazoans (nematodes and flatworms). Although SL addition in the kinetoplastida and a subset of nematode genes serves to resolve multicistronic mRNAs into monocistronic, capped mRNAs, information regarding the functional significance of trans-splicing in flatworms is limited. We describe here the identification and characterization of a closely linked gene upstream from the trans-spliced enolase gene in the flatworm Schistosoma mansoni. This gene produces a non-trans-spliced mRNA encoding a ubiquinol binding protein, UbCRBP, that is a component of the ubiquinol-cytochrome C reductase complex. The distance between the UbCRBP polyadenylation site and the enolase trans-splice acceptor site is exceptionally short, only 54 nucleotides. Primer extension (5' RACE), RT-PCR, and RNase mapping have identified steady state, cis-spliced RNAs which significantly overlap both the UbCRBP and enolase genes. These transcripts contain the 5' ends of mature UbCRBP mRNAs; extend through UbCRBP, across the intergenic region, and a significant distance 3' into the enolase gene. Interestingly, the close linkage between the UbCRBP and enolase genes is conserved in a second flatworm, Fasciola hepatica, which also trans-splices the downstream enolase gene. Taken together, the role of SL addition in resolving multicistronic transcripts in both C. elegans and the kinetoplastida, the conservation of UbCRBP/enolase gene linkage in two divergent trematodes, and the multicistronic organization of schistosome UbCRBP/enolase RNAs are consistent with the suggestion that these two genes are likely to be cotranscribed and that trans-splicing in flatworms may be associated with polycistronic transcripts.
Insights
Spliced leader trans-splicing in flatworms may resolve multicistronic transcripts. Researchers identified linked UbCRBP and enolase genes, suggesting cotranscription and a role for trans-splicing in gene expression regulation.
Area of Science:
- Molecular Biology
- Genetics
- Parasitology
Background:
- Spliced leader (SL) trans-splicing adds a small exon to pre-mRNAs in select organisms.
- SL trans-splicing resolves multicistronic into monocistronic mRNAs in some species.
- The function of trans-splicing in flatworms remains largely unexplored.
Purpose of the Study:
- To identify and characterize genes associated with trans-splicing in the flatworm Schistosoma mansoni.
- To investigate the functional significance of trans-splicing in flatworm gene expression.
- To explore the potential for cotranscription and resolution of multicistronic transcripts.
Main Methods:
- Primer extension (5' RACE)
- Reverse transcription polymerase chain reaction (RT-PCR)
- RNase mapping
Main Results:
- Identified a gene encoding ubiquinol binding protein (UbCRBP) upstream of the trans-spliced enolase gene.
- Discovered cis-spliced RNAs overlapping both UbCRBP and enolase genes.
- Observed conserved linkage between UbCRBP and enolase genes in Fasciola hepatica, suggesting cotranscription.
Conclusions:
- The close linkage and transcript overlap suggest cotranscription of UbCRBP and enolase genes in flatworms.
- Trans-splicing in flatworms may be associated with the resolution of polycistronic transcripts.
- This finding provides insights into gene expression mechanisms in parasitic flatworms.