Cloning and characterization of a gene encoding pig epidermal growth factor

A portion of the pig epidermal growth factor (EGF) gene has been isolated and characterized. The nucleotide sequencies of exons 20 and 21, which encode the EGF region of the precursor protein, show 85% similarity with the human EGF gene sequence. In addition, conservation of the intron-exon boundaries between the two species was generally observed. Although the pig exon 21 appeared to lack a single nucleotide at its 5' end relative to the human gene, sequences obtained by direct amplification of the genomic DNA around the 5' end of this exon using the polymerase chain reaction, and from a pig EGF cDNA recombinant isolated from a kidney library, indicated that the deletion was probably a cloning artifact. Comparison of the predicted amino acid sequence of pig EGF with that of EGF from other species, as well as with several other polypeptides which bind to the EGF receptor, indicated conservation of Gly18, Tyr37, Gly39 and Arg41 in addition to all six cysteine residues and Leu47, which are known to be critical for biological activity. A synthetic gene encoding the predicted amino acid sequence of pig EGF was expressed in yeast. The recombinant polypeptide was shown to compete with 125I-labelled mouse EGF for binding to cells and to stimulate DNA synthesis in quiescent monolayers of Swiss 3T3 cells.