Identification of a form of the avian erythroblastosis virus erb-B gene product at the cell surface

Abstract

Avian erythroblastosis virus (AEV) induces both erythroblastosis and fibrosarcoma in chickens¹. The viral oncogene responsible for these diseases, erb, is divided into two regions, erb-A and erb-B, although recent evidence suggests that it is primarily the erb-B gene product that is responsible for the transforming activity^2–5. The erb-B gene product has been reported previously to be a membrane glycoprotein of 68,000 molecular weight (MW), gp68^erb-B (refs 6, 7). However, we show here that gp68^erb-B is an in tracei lu lar precursor which is modified further to a 74,000 MW protein, gp74^erb-B. By the criteria of resistance to digestion with endoglycosidase H, subcellular fractionation and inhibition of biosynthesis by the ionophore monensin, gp74^erb-B appears to be located at the cell surface. Recently, a comparison of the erb-B sequence⁸ with that of the epidermal growth factor (EGF) receptor has shown that these two genes are highly homologous⁹, and that erb-B appears to represent a truncated form of this growth factor. In light of these data the identification of gp74^erb-B at the plasma membrane suggests that this may be the functionally important form of the erb-B gene product.