Sequence analysis of 5.4 kilobases (kb) of DNA upstream of the ATG initiation codon of the troponin I (TnI) gene of the ascidian Ciona intestinalis failed to identify a sequence corresponding to the first 16 nucleotides (nt) at the 5' end of the mature TnI mRNA. Database searching revealed that three additional and unrelated Ciona mRNAs contained the same, or almost identical, 16 nt sequence at the 5' -end. Reverse-transcriptase/polymerase chain reaction (RT-PCR) experiments proved that at least three additional mRNAs contain the same 5' -end sequence. These results suggested the possibility that the 5 ' end of the TnI, and other, Ciona mRNAs is derived by spliced leader (SL) trans-splicing. Also consistent with SL trans-splicing were Ciona embryo transfect ion studies with a TnI/beta-galactosidase reporter construct that demonstrated the existence of a functional TnI promoter within 1.5 kb of ATG-upstream DNA Moreover, RT-PCR experiments showed that TnI/beta-galactosidase transcripts contained the 16 nt mRNA common 5' end sequence despite the absence of this sequence from the transcriptional template construct. / This data is a demonstration of SL trans-splicing and represents the first reported case of SL trans-splicing among the deuterostomes. It suggests that SL trans-splicing may represent an ancestral metazoan feature. Moreover, because vertebrates probably arose from ascidian-like ancestors, it may be that many vertebrate genes, none of which are thought to undergo SL trans-splicing, are descended from trans-spliced ancestral genes. Such a history could explain the common occurrence in vertebrate genes of 5' untranslated region enhancer-containing introns.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.30761 |
| Date | January 1999 |
| Creators | Vandenberghe, Amanda. |
| Contributors | Hastings, Kenneth (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001746305, proquestno: MQ64472, Theses scanned by UMI/ProQuest. |
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