Human Islet Amyloid Polypeptide Gene: Complete Nucleotide Sequence, Chromosomal Localization, and Evolutionary History

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Abstract
The gene-encoding human islet amyloid polypeptide (hIAPP), a recently discovered 37 amino acid hormone-like polypeptide which is expressed in the insulin-producing β-cells of the endocrine pancreas, has been isolated and characterized. The coding region of the gene is interrupted in the 5′-untranslated region and NH2-terminal propeptide by introns of 330 and 4808 base pairs (bp), respectively. Exon 1 (104 bp) encodes most of the 5′-untranslated region of the mRNA; exon 2 (95 bp) encodes 15 nucleotides of 5′-untranslated region, the putative 22 amino acid signal peptide and five residues of the NH2-terminal propeptide; exon 3 (1246 bp) encodes the remainder of the NH2-terminal propeptide (residues 6–9), the IAPP moiety and its processing signals and the 16 amino acid COOH-terminal propeptide, as well as the 3′-untranslated region of the mRNA (1059 bp). Analysis of the nucleotide and predicted amino acid sequence of intron 2 of the hIAPP gene did not reveal any homology with the structurally related calcitonin/calcitonin-gene-related peptide genes and indicates that, in contrast to these latter genes, the hIAPP gene apparently gives rise to only a single hormonal product. The transcriptional initiation site was identified about 28 bp downstream from a TATAA sequence. The hIAPP gene was localized to the p12.3 region of chromosome 12.