Nucleic Acids Research, Vol 26, Issue 19 4516-4523, Copyright © 1998 by Oxford University Press
J Bouck, S Litwin, AM Skalka and RA Katz
Retroviruses utilize balanced splicing to express multiple proteins from a
single primary transcript. A number of cis -acting signals help maintain
this balance, including the branch point sequence (BPS), polypyrimidine
tract (PPyT) and sequences within the downstream exon. In general,
regulated splicing requires weak splicing signals and we have previously
shown the same requirement for the simple retrovirus, avian sarcoma virus
(ASV). Here we take advantage of the requirement for balanced splicing in
retroviral replication to examine the sequence constraints of an intronic
splicing element. Selection for replication competence makes it possible to
amplify and identify functional sequences from a pool of all possible
sequences. In this report we examine the role of pyrimidines within the
PPyT. Our results provide in vivo confirmation that the functional strength
of a PPyT is related to its length and uridine content and that the PPyT
plays a role in the second step of the splicing reaction. We also show that
the minimal distance between the 3'-splice site and the BPS in this system
is 16 nt. With modification, the selection system described here can be
used to examine the sequence constraints of other exonic or intronic
splicing elements in vivo .
ARTICLES
In vivo selection for intronic splicing signals from a randomized pool
Institute for Cancer Research, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA.
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