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Mol. Cell. Biol., Apr 1997, 2143-2150, Vol 17, No. 4
LR Coulter, MA Landree and TA Cooper
In vitro selection strategies have typically been used to identify a
preferred ligand, usually an RNA, for an identified protein. Ideally, one
would like to know RNA consensus sequences preferred in vivo for as-
yet-unidentified factors. The ability to select RNA-processing signals
would be particularly beneficial in the analysis of exon enhancer sequences
that function in exon recognition during pre-mRNA splicing. Exon enhancers
represent a class of potentially ubiquitous RNA- processing signals whose
actual prevalence is unknown. To establish an approach for in vivo
selection, we developed an iterative scheme to select for exon sequences
that enhance exon inclusion. This approach is modeled on the in vitro SELEX
procedure and uses transient transfection in an iterative procedure to
enrich RNA-processing signals in cultured vertebrate cells. Two predominant
sequence motifs were enriched after three rounds of selection: a
purine-rich motif that resembles previously identified splicing enhancers
and a class of A/C-rich splicing enhancers (ACEs). Individual selected ACEs
enhanced splicing in vivo and in vitro. ACE splicing activity was competed
by RNAs containing the purine-rich splicing enhancer from cardiac troponin
T exon 5. Thus, ACE activity is likely to require a subset of the SR
splicing factors previously shown to mediate activity of this purine- rich
enhancer. ACE motifs are found in two vertebrate exons previously
demonstrated to contain splicing enhancer activity as well as in the
well-characterized Drosophila doublesex (dsx) splicing enhancer. We
demonstrate that one copy of the dsx repeat enhances splicing of a
vertebrate exon in vertebrate cells and that this enhancer activity
requires the ACE motif. We suggest the possibility that the dsx enhancer is
a member of a previously unrecognized family of ACEs.
Copyright © 1997, American Society for Microbiology
Identification of a new class of exonic splicing enhancers by in vivo selection [published erratum appears in Mol Cell Biol 1997 Jun;17(6):3468]
Department of Pathology, Baylor College of Medicine, Houston, Texas 77030, USA.
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