Effect of a pseudo-5′ splice site in exon 16.

Presence of a pseudo-5′ splice site in exon 16 does not negatively regulate splicing at the authentic 5′ splice site. (A) Sequence of the cryptic splice site in exon 16. The similarity to a consensus 5′ splice site and its ability to be activated in construct 13/16i17 suggest that U1 snRNP can bind here. Also shown is a gt-> ca mutation introduced to block potential U1 binding. (B) Splicing of 3-exon constructs containing the cryptic splice site (lane 1) or its mutated variant (lane 2). The failure of the mutation to activate exon 16 inclusion argues against a model in which U1 binding at the cryptic site represses exon 16 splicing by inhibiting recognition of the authentic 5′ splice site.