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Molecular and Cellular Biology, October 1998, p. 5930-5941, Vol. 18, No. 10
Institute of Molecular Medicine, John
Radcliffe Hospital, Headington, Oxford OX3 9DS, United
Kingdom,1 and
Laboratoire
d'Immunogénétique Moléculaire, Institut de
Génétique Moléculaire CNRS UMR/G H5535, 34293 Montpellier Cedex 5, France,2
Received 17 February 1998/Returned for modification 15 April
1998/Accepted 9 July 1998
Although the splicing of transcripts from most eukaryotic genes
occurs in a constitutive fashion, some genes can undergo a process of
alternative splicing. This is a genetically economical process which
allows a single gene to give rise to several protein isoforms by the
inclusion or exclusion of sequences into or from the mature mRNA. CD44
provides a unique example; more than 1,000 possible isoforms can be
produced by the inclusion or exclusion of a central tandem array of 10 alternatively spliced exons. Certain alternatively spliced exons have
been ascribed specific functions; however, independent regulation of
the inclusion or skipping of each of these exons would clearly demand
an extremely complex regulatory network. Such a network would involve
the interaction of many exon-specific trans-acting factors
with the pre-mRNA. Therefore, to assess whether the exons are indeed
independently regulated, we have examined the alternative exon content
of a large number of individual CD44 cDNA isoforms. This analysis shows that the downstream alternatively spliced exons are favored over those
lying upstream and that alternative exons are often included in blocks
rather than singly. Using a novel in vivo alternative splicing assay,
we show that intron length has a major influence upon the alternative
splicing of CD44. We propose a kinetic model in which short introns may
overcome the poor recognition of alternatively spliced exons. These
observations suggest that for CD44, intron length has been exploited in
the evolution of the genomic structure to enable tissue-specific
patterns of splicing to be maintained.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Influence of Intron Length on Alternative Splicing
of CD44

*
Corresponding author. Mailing address: Institute of
Molecular Medicine, John Radcliffe Hospital, Headington, Oxford OX3
9DS, United Kingdom. Phone: 01865 221609. Fax: 01865 222502. E-mail: GScreaton{at}worf.molbiol.ox.ac.uk.
Present address: Laboratoire d'Immunogénétique
Moléculaire, Universite Montpellier II, UPR CNRS 1142, IGH, 34396 Montpellier Cedex 5, France.
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