Nucleic Acids Research Advance Access published online on January 18, 2008
Nucleic Acids Research, doi:10.1093/nar/gkm1147
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Molecular Biology |
Insights into the selective activation of alternatively used splice acceptors by the human immunodeficiency virus type-1 bidirectional splicing enhancer
1Institut für Virologie, Universitätsklinikum Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf and 2Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie, Martinistrasse 52, D-20251 Hamburg, Germany
*To whom correspondence should be addressed. Tel: +49 211 81 12393; Fax: +49 211 81 12227; Email: schaal{at}uni-duesseldorf.de
Received August 6, 2007. Revised November 9, 2007. Accepted December 11, 2007.
The guanosine-adenosine-rich exonic splicing enhancer (GAR ESE) identified in exon 5 of the human immunodeficiency virus type-1 (HIV-1) pre-mRNA activates either an enhancer-dependent 5' splice site (ss) or 3' ss in 1-intron reporter constructs in the presence of the SR proteins SF2/ASF2 and SRp40. Characterizing the mode of action of the GAR ESE inside the internal HIV-1 exon 5 we found that this enhancer fulfils a dual splicing regulatory function (i) by synergistically mediating exon recognition through its individual SR protein-binding sites and (ii) by conferring 3' ss selectivity within the 3' ss cluster preceding exon 5. Both functions depend upon the GAR ESE, U1 snRNP binding at the downstream 5' ss D4 and the E42 sequence located between these elements. Therefore, a network of cross-exon interactions appears to regulate splicing of the alternative exons 4a and 5. As the GAR ESE-mediated activation of the upstream 3' ss cluster also is essential for the processing of intron-containing vpu/env-mRNAs during intermediate viral gene expression, the GAR enhancer substantially contributes to the regulation of viral replication.