Expression and Characterization of Kinase‐active v‐erbB Protein Using a Baculovirus Vector System

The v‐erbB gene is an oncogene of the avian erythroblastosis virus encoding a protein that is a truncated version of the epidermal growth factor receptor. The v‐erbB protein was expressed alone or as polyhedrin‐erbB fusion proteins using the Bombyx mori nuclear polyhedrosis virus vector. The expression level of the fusion protein whose polyhedrin portion consisted of only 8 amino‐terminal amino acids was more than ten times higher than that of the non‐fusion protein. Studies with tunkamycin showed that the recombinant v‐erbB proteins were glycosylated. The recombinant protein autophosphorylated tyrosine residues, and phosphorylated a synthetic tyrosine‐containing peptide and lipocortin I. These observations indicate that functional v‐erbB protein can he expressed in silkworm‐derived cells, and furthermore, that this system can be used for large‐scale production.