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Molecular and Cellular Biology, March 2001, p. 1942-1952, Vol. 21, No. 6
Department of Molecular Biology, The Lerner
Research Institute, The Cleveland Clinic Foundation, Cleveland,
Ohio 44195
Received 18 October 2000/Returned for modification 22 November
2000/Accepted 13 December 2000
U12-dependent introns containing alterations of the 3' splice site
AC dinucleotide or alterations in the spacing between the branch site
and the 3' splice site were examined for their effects on splice site
selection in vivo and in vitro. Using an intron with a 5' splice site
AU dinucleotide, any nucleotide could serve as the 3'-terminal
nucleotide, although a C residue was most active, while a U residue was
least active. The penultimate A residue, by contrast, was essential for
3' splice site function. A branch site-to-3' splice site spacing of
less than 10 or more than 20 nucleotides strongly activated alternative
3' splice sites. A strong preference for a spacing of about 12 nucleotides was observed. The combined in vivo and in vitro results
suggest that the branch site is recognized in the absence of an active
3' splice site but that formation of the prespliceosomal complex A
requires an active 3' splice site. Furthermore, the U12-type
spliceosome appears to be unable to scan for a distal 3' splice site.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.6.1942-1952.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Role of the 3' Splice Site in U12-Dependent
Intron Splicing
*
Corresponding author. Mailing address: Department of
Molecular Biology, NC-2, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195. Phone: (216)
445-2692. Fax: (216) 444-0512. E-mail: padgetr{at}ccf.org.
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