Figure 4. Structures of the human ameloblastin (AMBN) and enamelin (ENAM) genes and their chromosomal localizations. Exons are indicated by numbered boxes, introns by a line. The numbers below each exon show the range of amino acids encoded by that exon. The AMBN gene has 13 exons, all coding. AMBN exons 7 through 9 are repeat sequences (Toyosawa et al., 2000). The human ENAM gene is shown with 10 exons for consistency with the mouse enamelin gene (Hu et al., 2001b). It is not known if exon 2, which is noncoding, is used in humans. The enamelin gene has 8 coding exons. The AMBN and ENAM genes are located together on the long arm of chromosome 4. The order of the genes is centromere, AMBN, ENAM, DSPP, DMP1, teleomere.