Nucleotide sequence analysis identifies the human c-sis proto-oncogene as a structural gene for platelet-derived growth factor

The simian sarcoma virus transforming gene, v-sis, encodes a protein, p28sis , that is closely related to human platelet-derived growth factor (PDGF). The human locus related to v-sis was cloned and shown to contain at least five exons corresponding to the v-sis coding region. Nucleotide sequence analysis of these exons revealed that the predicted amino acid sequence of human c-sis differed by 6% from that of the woolly monkey-derived v-sis. These findings imply that the sis proto-oncogene has been well conserved during primate evolution. By comparison of the known amino acid sequences of PDGF peptides with the predicted human c-sis protein, it was possible to demonstrate that this human proto-oncogene is the structural gene encoding one of the two major polypeptides of this potent mitogen for connective tissue cells.