Identity of human epidermal growth factor (EGF) receptor with glycoprotein SA-7: evidence for differential phosphorylation of the two components of the EGF receptor from A431 cells.

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Abstract
A 165-kilodalton (kDal) surface glycoprotein encoded by human chromosome 7 (SA-7) had been characterized by using antisera raised against human chromosome 7-containing somatic cell hybrids. Evidence that SA-7 is the human receptor for epidermal growth factor (EGF) and that these antisera recognize human-specific determinants is presented. The gene coding for the human EGF receptor is localized to the p12 to p22 region of chromosome 7. The 145-kDal/165-kDal EGF receptor doublet of human epidermoid carcinoma A431 cells was characterized after immunoprecipitation of radiolabeled cell extracts with these antisera. A protein with endogenous kinase activity copurifies with the A431 receptor doublet and both components of the doublet contain phosphotyrosine and phosphothreonine and the 165-kDal component contains phosphoserine as well. Although each component of the receptor doublet has an average pI of 7, both display charge heterogeneity and appear to have unique charge isomers. The relationship between the 2 components of the A431 EGF receptor is discussed.