Epstein-Barr virus induction by a serum factor. Characterization of the purified factor and the mechanism of its activation.

Purified Epstein-Barr virus-inducing factor shows all the properties previously described for crude serum, i.e. inducing activity, cooperative activity with the inducers 12-O-tetradecanoyl-phorbol-13-acetate, 5'-iodo-2'-deoxyuridine, N-butyric acid, anti-IgM, and the need to be activated by pH shock. A small subpopulation of untreated factor molecules is fully active, however. The factor is a protein that is characterized by considerable heat resistance and sensitivity to reducing agents. It does not seem to require sugar residues or lipid for its activity. Activation occurs both at alkaline and acidic pH. Inactive and activated factor differ in their sensitivity to trypsin and in the degree of sensitivity to reducing agents. A change of conformation within the molecule seems to be the biochemical basis for the activation reaction.