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Molecular and Cellular Biology, December 1998, p. 7510-7520, Vol. 18, No. 12
Department of Biochemistry, University of
Leicester, Leicester LE1 7RH, United Kingdom
Received 4 June 1998/Returned for modification 10 August
1998/Accepted 31 August 1998
Efficient splicing of the 5'-most intron of pre-mRNA requires a 5'
m7G(5')ppp(5')N cap, which has been implicated in U1 snRNP
binding to 5' splice sites. We demonstrate that the cap alters the
kinetic profile of U1 snRNP binding, but its major effect is on U6
snRNA binding. With two alternative wild-type splice sites in an
adenovirus pre-mRNA, the cap selectively alters U1 snRNA binding at the
site to which cap-independent U1 snRNP binding is stronger and that is
used predominantly in splicing; with two consensus sites, the cap acts
on both, even though one is substantially preferred for splicing.
However, the most striking quantitative effect of the 5' cap is neither
on U1 snRNP binding nor on the assembly of large complexes but on the
replacement of U1 snRNP by U6 snRNA at the 5' splice site. Inhibition
of splicing by a cap analogue is correlated with the loss of U6
interactions at the 5' splice site and not with any loss of U1 snRNP binding.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
The Pre-mRNA 5' Cap Determines Whether U6 Small
Nuclear RNA Succeeds U1 Small Nuclear Ribonucleoprotein Particle at
5' Splice Sites
*
Corresponding author. Mailing address: Department of
Biochemistry, University of Leicester, Leicester LE1 7RH, United
Kingdom. Phone: (116) 2523482. Fax: (116) 2523369. E-mail:
eci{at}le.ac.uk.
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