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Molecular and Cellular Biology, December 1999, p. 8263-8271, Vol. 19, No. 12
Gene Expression Programme, European Molecular
Biology Laboratory, D-69117 Heidelberg,
Germany,1 and Department of Molecular
and Cellular Biology, Harvard University, Cambridge, Massachusetts
021382
Received 2 July 1999/Returned for modification 31 August
1999/Accepted 13 September 1999
U2 snRNP auxiliary factor (U2AF) promotes U2 snRNP binding to
pre-mRNAs and consists of two subunits of 65 and 35 kDa,
U2AF65 and U2AF35. U2AF65 binds to
the polypyrimidine (Py) tract upstream from the 3' splice site and
plays a key role in assisting U2 snRNP recruitment. It has been
proposed that U2AF35 facilitates U2AF65 binding
through a network of protein-protein interactions with other splicing
factors, but the requirement and function of U2AF35 remain
controversial. Here we show that recombinant U2AF65 is
sufficient to activate the splicing of two constitutively spliced
pre-mRNAs in extracts that were chromatographically depleted of U2AF.
In contrast, U2AF65, U2AF35, and the
interaction between them are required for splicing of an immunoglobulin µ pre-RNA containing an intron with a weak Py tract and a purine-rich
exonic splicing enhancer. Remarkably, splicing activation by
U2AF35 occurs without changes in U2AF65
cross-linking to the Py tract. These results reveal substrate-specific requirements for U2AF35 and a novel function for this
factor in pre-mRNA splicing.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Evidence for Substrate-Specific Requirement of the
Splicing Factor U2AF35 and for Its Function after
Polypyrimidine Tract Recognition by U2AF65
*
Corresponding author. Mailing address: Gene Expression
Programme, European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany. Phone: 49-6221-387 156. Fax: 49-6221-387 518. E-mail: juan.valcarcel{at}embl-heidelberg.de.
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