Fig. 5. Modular exon organization of the Ncad gene. The Ncad gene contains 21 exons that span approximately 100 Kb of genomic DNA. Mutually exclusive alternative splicing occurs in exons 7, 13, and 18. As deduced from cDNA sequences, mature mRNA contains exon 7a or 7b, exon 13a or 13b, and exon 18a or 18b. In addition, exon 7a' is found in some exon 7a-containing transcripts. Constant exons are shown as red boxes and alternative exons as green (7a,13a,18a) or blue (7b,13b,18b) boxes. Exons 7a and 7b each encodes the C-terminal half of CA8 and the N-terminal half of CA9; exons 13a and 13b each encode the C-terminal half of CA11 and the N-terminal half of CA12; exons 18a and 18b each encode the C-terminal half of EGF-CA3, the entire EGF-CA4, and the N-terminal half of the TM. The exon 7a' encodes an insertion of four amino-acid residues in CA8. The amino-acid sequence identity between the regions encoded by the alternative exons is indicated. SP: signal peptide; CA: cadherin domain; EGF: EGF-like calcium-binding repeat; LamG: Laminin-G-like domain; TM: transmembrane region; CP: cytoplasmic domain containing ß-catenin binding site.