FIG. 6.

Fox1 proteins enhance Exon 33 splicing in the Dup-E33 minigene transcripts. (A) Diagram of the Dup-E33 minigene. The downstream Fox binding element and its mutations (mut 1 or mut 2) are indicated. Dup-E33 minigene contains 1079 nt of rat genomic sequence surrounding exon 33, including 721 nucleotides of the upstream intron, the 33-nucleotide exon, and 325 nucleotides of the downstream intron (see Fig. S3B in the supplemental material). (B) Primer extension assay of exon 33 splicing in HEK293T cells cotransfected with Dup-E33 or its mutants, together with increasing amounts of Fox2 plasmids. Coexpressed Fox2 protein enhances exon 33 splicing in transcripts from the Dup-E33 minigene (lanes 1 to 4). This enhancement was eliminated by the Fox binding element mutations (lanes 5 to 8 and lanes 9 to 12). Fox2 overexpression was assayed by immunoblotting with anti-Fox RRM antibody, shown at the bottom. α, anti.