“…To date, nine retroviral oncogene products (v-src, v-yes, vfgr, v-fps/fes, v-abl, v-ros, v-erbB, v-fms and v-sea) have been shown to exhibit protein-tyrosine kinase (PTK) activity (Hayman et al, 1985;Hunter & Cooper, 1985;Kris et al, 1985;Barbacid et al, 1981). The amino acid sequence responsible for PTK activity (kinase domain was initially identified in the v-src protein (Collett et al, 1980;Hunter & Sefton, 1980;Levinson et al, 1980) and has been shown to be conserved in the other eight oncogene-encoded proteins (Hunter, 1985).…”