Schematic representations of TGS, trappin , SLPI , and the trappin -related gene. (A) The three-exon structure of mammalian TGS and trappin genes and the four-exon structure of mammalian SLPI gene are shown. (B) Structure of the trappin-related genes of chicken and opossum (upper) and platypus SLPI gene (lower). The homologous regions are shown by dotted lines. The exons are shown by boxes. TGS- and WAP-coding exons are indicated by light and dark gray, respectively. The signal-peptide-coding regions and noncoding regions are indicated by black and white boxes, respectively. S, signal-peptide-coding region.