Identification and characterization of the avian erythroblastosis virus erbB gene product as a membrane glycoprotein

Avian erythroblastosis virus causes erythroid leukemia and sarcomas in chickens. The viral oncogene responsible for these diseases, erb, is divided into two regions known as erbA and erbB, and recent evidence suggests that it is the erbB gene that is responsible for the transforming activity. From rats bearing avian erythroblastosis virus-induced sarcomas, we have obtained antisera which are specific for the erb gene products. Using such antisera, we have been able to characterize the erbB gene product as a 68,000 molecular weight protein. Pulse-chase and cell-free in vitro translation experiments show that the initial product is a 62,500 dalton protein which is initially modified to a 66,000 dalton protein, and then further modified to a 68,000 dalton form. These modifications could be shown to be associated with glycosylation and phosphorylation. Cell fractionation experiments revealed that the 66,000 and 68,000 dalton proteins were located in cell membrane fractions, and immunofluorescence results showed the erbB gene product to be expressed on the cell surface.