Avian oncovirus proteins expressed on the surface of infected cells

Lactoperoxidase-catalyzed iodination and anti-AMV immunoprecipitation showed that both chicken and duck fibroblasts infected with a sarcoma virus (Rous sarcoma virus PrC) or a leukemia virus (avian myeloblastosis virus; AMV) had on their surface a protein of approximately 120 kilodaltons molecular weight (120K), as well as envelope glycoprotein precursors of 90–92 kd. Uninfected chicken fibroblasts of the gs^?, chf^? phenotype had much lower, but detectable amounts of surface 120K, whereas uninfected duck fibroblasts did not have any, suggesting a relationship between surface 120K and expression of chicken virus information in the cell. 120K is a glycoprotein, since it could be labeled with [³H]mannose and contained a component that bound to a concanavalin A affinity column. The 120K protein was characterized by tryptic fingerprinting after reiodination with chloramine-T. Total and Con A-selected 120K from infected chicken cells and total 120K from infected duck cells had essentially identical fingerprints. Moreover, they were extensively related to the iodinated fingerprint of Pr76^gag, the intracellular precursor of viral core proteins. These results indicate that expression on the cell surface of glycosylated forms of gag polyproteins occurs also in avian oncornavirus infections, similarly to findings in the murine leukemia virus system.