Evidence that a cytoplasmically located version of a v-erbB-encoded protein can transform both fibroblasts and erythroblasts.

We previously isolated an avian erythroblastosis virus, AEV-GEE35, in which the complete extracellular and transmembrane domains of the v-erbB oncoprotein were replaced with sequences from the gag and env proteins. The GEE35 virus was capable of transforming both fibroblasts and erythroblasts as efficiently as wild-type v-erbB. Analysis of the v-erbB proteins encoded by GEE35 revealed two proteins of similar molecular weights of approximately 130,000 Da. One of these proteins was an N-linked glycosylated membrane protein, whereas the other was a cytoplasmic protein. Biochemical characterization of these two proteins revealed that the transmembrane protein has the v-erbB domain outside the cell, such that it no longer had access to its tyrosine kinase substrates. This implies that it is the cytoplasmically located v-erbB-encoded protein that is responsible for the efficient transforming ability of this virus.