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Gastric inhibitory polypeptide (GIP) is a 42-amino acid hormone that stimulates insulin secretion in the presence of glucose. Complementary DNA clones encoding human GIP were isolated from a library prepared with RNA from duodenum. The predicted amino acid sequence indicates that GIP is derived by proteolytic processing of a 153-residue precursor, preproGIP. The GIP moiety is flanked by polypeptide segments of 51 and 60 amino acids at its NH2 and COOH termini, respectively. The former includes a signal peptide of about 21 residues and an NH2-terminal propeptide of 30 amino acids. GIP is released from the precursor by processing at single arginine residues. There is a region of nine amino acids in the COOH-terminal propeptide of the GIP precursor that has partial homology with a portion of chromogranin A as well as pancreastatin.Gastric inhibitory polypeptide (GIP) was first isolated from porcine small intestine (1, 2) on the basis of its ability to inhibit histamine-stimulated gastric acid secretion in the dog stomach (3). The sequences of porcine (4, 5), bovine (6), and human GIP (7) have been determined; each has 42 amino acids, and the sequence is highly conserved. The porcine and bovine peptides differ from the human at two and four sites, respectively. The sequence of GIP indicates that this peptide is a member of a family of structurally related hormones that includes secretin, glucagon, vasoactive intestinal peptide, and growth hormone-releasing factor (8-10). Subsequent studies of the physiological properties of GIP revealed that it was a relatively poor inhibitor of gastric acid secretion (11) but was a potent stimulator of insulin secretion (12, 13). It is able to stimulate insulin secretion at physiological concentration only in the presence of glucose (14,15). Thus, GIP by functioning as a glucose-dependent insulin-releasing peptide could have a role in maintaining glucose homeostasis. Moreover, it might also be of use in treating some diabetics. As a first step in studying the biosynthesis of this potentially important regulator of beta cell function, we have isolated and sequenced cDNA clones encoding the human GIP precursor. This report describes the sequence of these clones and the predicted amino acid sequence of the human protein. Fig. 1 were synthesized by a modification of the triester method (21). Probes I and II were end-labeled at the 5'-terminal end with T4 polynucleotide kinase (Toyobo, Osaka, Japan) and [y-32P]ATP (Amersham; 6000 Ci/mmol; 1 Ci = 37 GBq) and was purified by passing through a Sephadex G-50 (Pharmacia) column. MATERIALS AND METHODSColony Screening. Escherichia coli HB101 was transformed with the recombinant DNA by the calcium-shock procedure (22). Colony hybridization (23) was performed with probe I (14-mer) at 36°C for 18 hr and with probe II (17-mer) at 40°C for 18 hr in 4x NaCl/Cit (lx = 0.15 M NaCI/0.015 M sodium citrate, pH 7) containing 1OX Denhardt's solution (1x = 0.02% polyvinylpyrrolidone/ 0.02% Ficoll/0.2% bovine serum albumin), 0.1% NaDodSO4, 25 ,ug of...