What Causes the Increase in PK-i after Interferon

The mechanism by which interferon treatment increases the enzymatic phosphorylation of protein 67 and eIF-2 was investigated. The increase is seen at 5-6 hours after addition of interferon to mouse L cells and is blocked by actinomycin D. Since protein 67 is found in purified preparations of PK-i we wondered whether this protein is induced by interferon. Not having protein 67 substrate free of PK-i, we made use of the fact that in himian cells the interferon- and dsENA-induced equivalent of protein 67 migrates more slowly on SDS polyaciylamide gels (protein 69) (16). Addition 

Figoire 4 Arrow shows bond split by nuclease (see text). 

We also examined whether factor A could be alone responsible for the increased PK-i activity after interferon treatment. Factor A stimulated slightly eIF-2 and histone phosphorylation in control cell extracts but not nearly as much as in interferon-treated cell extracts. Factor A was found in control cell preparations. Some component of the protein kinase PK-i itself seems, therefore, to change after interferon treatment. Finally, protein phosphatase P is found both in control cell sap and, in lower amounts, in 

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