Abstract
Treatment of K/Balb cells with IdUrd leads to the expression of endogenous virus and interferon is formed which subsequently can suppress the release of virus into the medium. Under these conditions, a protein kinase activity capable of phosphorylating an endogenous polypeptide of apparent mol. wt. 67000 is detected. This kinase activity is analogous to that induced in K/Balb cells treated with exogenous interferon. The induction of the protein kinase activity in IdUrd-treated K/Balb cells can be blocked by anti-interferon serum, thus providing evidence for the presence and action of interferon.