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Portal, D., Espinosa J.M., Lobo G.S., Kadener S., Pereira C.A., De La Mata M., Tang Z., Lin R.-J., Kornblihtt A.R., Baralle F.E., Flawia M.M., and Torres H.N.. 2003. An Early Ancestor in The Evolution of Splicing: A Trypanosoma Cruzi Serine-arginine-rich Protein (TcSR) Is Functional in Cis-splicing. Molecular and Biochemical Parasitology 127: 37-46. Full Article

A novel serineľarginine-rich protein designated TcSR was identified in Trypanosoma cruzi. The deduced amino acid sequence reveals that TcSR is a member of the SR protein family of splicing factors that contains two RNA-binding domains at the N-terminal side and several serineľarginine repeats at the COOH-terminus. Over expression of either TcSR or the human SR-protein associated splicing factor/splicing factor 2 (ASF/SF2) in wild-type Schizosaccharomyces pombe, provoked an elongated phenotype similar to that of fission yeast over expressing the SR-containing splicing factor Prp2, a U2AF65 orthologue. When a double mutant strain lacking two SR protein-specific protein kinases was used, expression of TcSR or human SR ASF/SF2 splicing factor reverted the mutant to a wild-type phenotype. Transient expression of TcSR in HeLa cells stimulated the inclusion of the EDI exon of human fibronectin in an in vivo functional alternative cis-splicing assay. Inclusion was dependent on a splicing enhancer sequence present in the EDI exon. In addition, TcSR and peptides carrying TcSR-RS domain sequences were phosphorylated by a human SR protein kinase. These results indicate that TcSR is a member of the SR splicing network and that some components common to the trans- and cis-splicing machineries evolved from the early origins of the eukaryotic lineage.

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