FIG. 4.

Gain-of-function assays for MSE2 and MSE3. MSE2(×3) contains three copies of MSE2 (positions +3 to +46 of intron 5) (Fig. 2) placed 16 nucleotides downstream from the 46-nucleotide heterologous exon. Upstream of the exon are the last 99 nucleotides of cTNT intron 4, which contains MSE1. MSE3(×3) and MSE3(×6) contain three or six copies of MSE3 (positions +57 to +90 of intron 5) (Fig. 2) placed 16 nucleotides downstream of the alternative exon. The MSE3 concatamers in MSE3mut(×6) contain the RTB66-81 mutation (Fig. 2). The percent of spliced mRNA that includes the alternative exon in fibroblasts (F) and muscle (M) is indicated with standard deviation and number of transfections (n). Whether splicing is (+) or is not (−) regulated in muscle (REG) is also indicated.