Gene linkage and steady state RNAs suggest trans-splicing may be associated with a polycistronic transcript in Schistosoma mansoni.
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.
Davis
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Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA. rdavis@murray.fordham.edu
Hodgson
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism; D014450:Electron Transport Complex III / Q000235:genetics; D005210:Fasciola hepatica / Q000201:enzymology / Q000235:genetics; D005784:Gene Amplification; D017238:Genes, Helminth; D008040:Genetic Linkage; D008969:Molecular Sequence Data; D010751:Phosphopyruvate Hydratase / Q000235:genetics; D012326:RNA Splicing; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics*; D012260:Ribonucleases; D012550:Schistosoma mansoni / Q000201:enzymology / Q000235:genetics*; D014158:Transcription, Genetic; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000378:metabolism
D002352:Carrier Proteins; D012333:RNA, Messenger; D014451:Ubiquinone; D012260:Ribonucleases; D010751:Phosphopyruvate Hydratase; D014450:Electron Transport Complex III; C003741:ubiquinol