Alpha coat protein COPA (HEP-COP): presence of an Alu repeat in cDNA and identity of the amino terminus to xenin.
We previously sequenced the 4333-nucleotide cDNA of the COPA (HEP-COP) gene which encodes the human homologue of the alpha-subunit of the coatomer protein complex, involved in intracellular protein transport. Within the 3' untranslated region at nucleotides 4049-4333 was observed an Alu repeat containing conserved A and B block elements, and showing high homology to the human Alu-Sx subfamily consensus sequence. Upstream of the Alu repeat were noted a TATA box, a CAAT motif and two activating transcription factor (ATF)-like binding sites, which represent putative regulatory elements directing Alu transcription. In addition, the 25 and 35 N-terminal amino acid residues of COPA and its bovine homologue were identical to xenin-25 and proxenin, respectively. Xenin-25 is a gastrointestinal hormone that stimulates exocrine pancreatic secretion. This peptide is related to xenopsin, neurotensin and neuromedin N which are bioactive peptides derived from larger precursors via proteolytic cleavage by cathepsin E at processing sites determined by conserved C-terminal sequences, i.e. proline/valine-X-X-hydrophobic amino acid. Given the conformity of the C-terminal residues of xenin-25 (PWIL) and of its progenitor molecule, proxenin (VIQL), it is proposed that these peptides are generated by a similar mechanism of post-translational modification involving a parent precursor represented by the alpha-subunit of coatomer.
Chow
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VT
Department of Microbiology, Faculty of Medicine, National University of Singapore, Singapore.
Quek
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HH
D001483:Base Sequence; D020756:Coatomer Protein; D018076:DNA, Complementary / Q000235:genetics*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009496:Neurotensin; D010455:Peptides / Q000235:genetics*; D011499:Protein Processing, Post-Translational; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D020756:Coatomer Protein; D018076:DNA, Complementary; D008565:Membrane Proteins; D010455:Peptides; C077659:xenin 25; D009496:Neurotensin