Structure determination and evolution of the chicken cDNA and gene encoding prepropancreatic polypeptide

We have previously demonstrated that the C-terminal regions of the rat and human pancreatic polypeptide (PPP) precursors exhibit a high degree of divergence, whereas the N-terminal regions are highly conserved. This blend of structural conservation and divergence in the precursors appears to be caused by splice junction sliding and translational frameshift in the 3'-region of the PPP gene Yonekura et al., J. Biol. Chem. 263 (1988) 2990–2997]. In the present study, we determined the nucleotide (nt) sequences of the chicken PPP (cPPP) cDNA and gene, and compared them with those of the mammals. In cPPP, the C-terminal region of the precursor is quite heterologous with respect to the rat (rPPP) and human (hPPP) precursors, and this heterogeneity is accentuated by the large deletion in exon 3 of cPPP. Furthermore, mutational accumulation during evolution caused the structural organization of the 3'-region of cPPP to change; cPPP is terminated in exon 3, whereas rPPP and hPPP are terminated in exon 4. Thus, our previous observation regarding the possibility of ‘mosaic evolution’ Yamamoto et al., J. Biol. Chem. 261 (1986) 6156–6159] of PPP has been extended and confirmed by this study. Available evidence suggests that ‘mosaic evolution’ is a phenomenon unique to PPP, and not to the genes encoding the other members of the PPP family, neuropeptide-Y and peptide-YY.