The exon sequence TAGG can inhibit splicing.

The fibroblast growth factor receptor-2 gene contains a pair of alternative exons, K-SAM and BEK, which are spliced in a cell type specific manner. We have shown previously that a 10 nucleotide sequence within the K-SAM exon exerts a negative effect on K-SAM exon splicing independent of cell type. We demonstrate here that this sequence works autonomously, as it can repress splicing of a heterologous exon, the EIIIb alternative exon of the rat fibronectin gene. By introducing point mutations into the 10 nucleotide sequence, we have shown that the functional portion is limited to 4 nucleotides, TAGG, the dinucleotide AG of which is particularly important. This short sequence may participate in the control of splicing of exons carrying it, provided that they carry weak splice sites.