Purification and characterization of vaccinia virus growth factor

A growth factor detected in the medium of vaccinia-virus-infected cells was purified to homogeneity. Sequence analysis shows it to be a processed form of a polypeptide encoded in the vaccinia virus genome which is related to epidermal growth factor (EGF) and alpha-transforming growth factor (alpha TGF). The amino terminus of the processed vaccinia virus growth factor (VVGF) begins at residue 20 of the primary translation product, indicating a signal sequence has been removed. The amino acid composition of purified VVGF predicts the carboxyl terminus is at, or near, residue 96, suggesting a transmembrane sequence has also been removed from secreted VVGF, which is, therefore, approximately 77 amino acids. VVGF, unlike EGF or alpha TGF, is glycosylated. VVGF binds to the EGF receptor and stimulates its autophosphorylation, suggesting that vaccinia virus has acquired sequences encoding a growth factor that may allow it to subvert EGF receptor-dependent functions.