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Mol Cell Biol, August 1998, p. 4620-4628, Vol. 18, No. 8
Departments of Internal
Medicine1 and
Cell
Biology,2 Yale University School of
Medicine, New Haven, Connecticut 06520-8022
Received 24 February 1998/Returned for modification 14 April
1998/Accepted 26 May 1998
Previous studies have identified a conserved AG dinucleotide at the
3' splice site (3'SS) and a polypyrimidine (pPy) tract that are
required for trans splicing of polycistronic pre-mRNAs in
trypanosomatids. Furthermore, the pPy tract of the Trypanosoma brucei
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Copyright © 1998, American Society for Microbiology. All rights reserved.
Exonic Sequences in the 5' Untranslated Region of
-Tubulin mRNA Modulate trans Splicing in
Trypanosoma brucei
-tubulin 3'SS region is required to specify accurate
3'-end formation of the upstream
-tubulin gene and trans
splicing of the downstream
-tubulin gene. Here, we employed an in
vivo cis competition assay to determine whether sequences
other than those of the AG dinucleotide and the pPy tract were required
for 3'SS identification. Our results indicate that a minimal
-tubulin 3'SS, from the putative branch site region to the AG
dinucleotide, is not sufficient for recognition by the
trans-splicing machinery and that polyadenylation is
strictly dependent on downstream trans splicing. We show
that efficient use of the
-tubulin 3'SS is dependent upon the
presence of exon sequences. Furthermore,
-tubulin, but not actin
exon sequences or unrelated plasmid sequences, can replace
-tubulin
exon sequences for accurate trans-splice-site selection.
Taken together, these results support a model in which the
informational content required for efficient trans splicing of the
-tubulin pre-mRNA includes exon sequences which are involved in modulation of trans-splicing efficiency. Sequences that
positively regulate trans splicing might be similar to
cis-splicing enhancers described in other systems.
*
Corresponding author. Mailing address: Department of
Internal Medicine, Yale University School of Medicine, P.O. Box 208022, 333 Cedar St., New Haven, CT 06520-8022. Phone: (203) 785-3563. Fax:
(203) 785-3864. E-mail: elisabetta.ullu{at}yale.edu.
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