Fig. 4.
Sequence requirements for splicing of introns flanking exon 16.
(A) Oocyte splicing assays. Left: excision of the upstream intron in the presence of downstream intron sequences (lane 1) or in the presence of juxtaposed exon 17 sequences (lane 2). Removal of the upstream intron was assayed by PCR with the use of primers in E13 (oligo S1) and E16 (AS2). Right: excision of the downstream intron in the presence of upstream intron sequences (lane 3) or in the presence of juxtaposed exon 13 sequences (lane 4). Removal of the downstream intron was assayed by PCR with the use of primers in E16 (oligo S2) and E17 (AS3). (B) Summary of results. Most importantly, excision of the downstream intron was most accurate if it occurred in conditions consistent with first step removal, ie, in the presence of the upstream intron (construct i16i17). Excision of the upstream intron appeared most efficient as a second step reaction (construct 13i16/17). The product slightly larger than the authentic spliced band represents a potential cryptic splicing event that was predominantly formed when splicing of the upstream intron was attempted as a first step (lane 1).