FIG. 3.

Specificity of the caldesmon enhancer requires the entire enhancer monomer. Precursor RNAs similar to those diagrammed in Fig. 2 containing the entire caldesmon enhancer, the 5′ half of the enhancer (nucleotides 1 to 16 of the sequence shown in Fig. 1A), or the 3′ half of the enhancer (nucleotides 17 to 32 of the sequence shown in Fig. 1A) were prepared. Reaction products resulting from splicing using the exon-internal (IS) or exon-terminal (TS) 5′ splice site are indicated. The gel used for this experiment has a different cross-linking ratio than that in Fig. 2, causing lariat species to migrate just above the TS band representing double splicing using the terminal 5′ splice site.