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Molecular and Cellular Biology, March 2001, p. 1509-1514, Vol. 21, No. 5
Department of Cell Biology, Harvard Medical
School, Boston, Massachusetts 02115
Received 31 July 2000/Returned for modification 14 September
2000/Accepted 5 December 2000
Specific mechanisms must exist to ensure fidelity in selecting the
AG dinucleotide that functions as the 3' splice site during the second
transesterification step of splicing. Here we show that the optimal
location for this AG is within a narrow distance (19 to 23 nucleotides
[nt]) downstream from the branch point sequence (BPS). Contrary to
previous expectations, AGs located less than 23 nt from the BPS are
always recognized, even when a second AG located more optimally
downstream is used in the transesterification reaction. Indeed, the AG
closest to the BPS actually dictates the precise location of the AG
that engages in the reaction. This mechanism, in which the AG is
identified by a general localization step followed by a precise
localization step, may be used to achieve fidelity while allowing
flexibility in the location of 3' splice sites.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.5.1509-1514.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
An Upstream AG Determines Whether a Downstream AG
Is Selected during Catalytic Step II of Splicing
*
Corresponding author. Mailing address: Department of
Cell Biology, Harvard Medical School, Boston, MA 02115. Phone: (617) 432-2844. Fax: (617) 432-3091. E-mail:
rreed{at}hms.harvard.edu.
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