Periostin and TGFBI exon and domain structure. Numbered periostin (POSTN) and TGFBI exons (coding sequence only) are displayed to scale. Amino acid (AA) position scales and hydrophobicity profiles (adapted from the UCSC proteome browser ) for either protein are displayed above and below the exon structures, respectively. Domains and features in common are displayed in-between: a signal sequence (ss), an EMI domain, and four FAS1 domains. Vertical black bars in FAS1 domains 2 and 4 mark the integrin binding sites with conserved central DI dimers. The shaded regions in the N-terminal end of the FAS1 domains represent γ-glutamylcarboxylase recognition sites. Additional features specific to either of the two proteins are indicated by markers positioned in the respective exon structure as follows. Pink diamond: POSTN N-glycosylation site; blue triangle: TGFBI integrin RGD binding site; green oval: POSTN heparin binding motif (suspected); purple rectangle: POSTN bipartite nuclear localization signal. The two orange V's mark sites of genomic variation in periostin of other tetrapods: between exons 19 and 20, a cluster of 8 additional exon 19 copies observed in X. tropicalis, and an additional exon "21V22" between exons 21 and 22, observed for example in chicken. The periostin region between exons 16 and 22 is flagged as subject to widespread alternative splicing ("AS"), and the extent of the "C-terminal region" as referred to in this work is indicated. See the main text for detailed descriptions.