The structure and biosynthesis of epidermal growth factor precursor

The structure of mouse submaxillary gland epidermal growth factor (EGF) precursor has been deduced from complementary DNAs. The mRNA is approximately 4800 bases and predicts prepro EGF to be a protein of 1217 amino acid residues (133 X 10 Mr). EGF (53 amino acid residues) is flanked by polypeptides of 188 and 976 residues at its carboxy and amino termini, respectively. The amino terminus of the precursor contains seven cysteine-rich peptides that resemble EGF. Towards the carboxy terminus is a 20-residue hydrophobic membrane spanning domain. The mild portion of the EGF precursor shares a 33% homology with the low density lipoprotein receptor, which extends over 400 amino acid residues. These features suggest that EGF precursor could function as a membrane-bound receptor. RNA dot-blot analysis and in situ hybridization show EGF mRNA to be abundant in the submaxillary gland, kidney and incisor tooth buds. Lower EGF mRNA levels were found in the lactating breast, pancreas, small intestine, ovary, spleen, lung, pituitary and liver. In the kidney EGF mRNA was most abundant in the distal convoluted tubules. Analysis of EGF precursor biosynthesis in organ culture of the submaxillary gland and kidney showed differential processing of the precursor in the two tissues. In the submaxillary gland immunoreactive low molecular weight EGF was produced, but in the kidney the high molecular weight precursor was not processed. In the distal convoluted tubule of the kidney EGF precursor may act as a receptor that is involved in ion transport.