Figure 2.

Structures and intron phases. White, gray, and black regions represent UTR, SP, and the mature protein, respectively. (A) Exon–intron structures of EMP, casein, and salivary protein genes on 4q13 and AMEL on Xp22 are shown. The length of each exon (bp) is shown in the boxes. The phases of introns are indicated at the bottom of exon boundaries. CSN1S2L2 is a pseudogene, but the exon–intron boundaries were determined unambiguously by comparing bovine and porcine CSN1S2 sequences with the human genome sequence. (B) Exon–intron structures of SPARCL1 and dentine/bone ECM protein genes on 4q21 are shown. The structure of SPARC is the same as SPARCL1 except that exon 4 is missing in the 5′ region of SPARC. (C) The structure of the first four exons of the primordial EMP gene is shown. A protein kinase phosphorylates the Ser residue (P) in the SXE motif coded by the 3′ end of exon 3. The introns are exclusively phase-0.