Interferons are glycoproteins whose synthesis is induced in various animal cells upon infection by any of a large variety of viruses or treatment with other inducers. The interferons are released from the producing cells, become attached to other cells and impair in these the replication of a large variety of viruses. We are studying the molecular basis of this impairment. Many of our studies are performed with mouse Ehrlich ascites tumor cells and mouse L929 firbroblasts. Extracts from interferon treated cells (S30INT) differ from extracts of control cells (S30C) in various biochemical characteristics. 1) Viral mRNAs degraded faster in S30INT than in S30C but only if the extracts are supplemented with double-stranded RNA and ATP. This degradation is catalyzed by an endonuclease system. The mediators in the activation of this system by double-stranded RNA and ATP are 2'5' linked oligoadenylates. We are purifying this endonuclease and plan to determine its cleavage specificity. 2) Double-stranded RNA promotes the phosphyorylation by ATP of several proteins in S30 INT and to only a much lesser extent in S30C. One of the proteins phosphorylated is a subunit of the peptide chain initiation factor eIF-2. We are attempting to identify a 67,000 dalton protein also phsophorylated by this system. 3) We are attempting to test if interferon induces the formation of new proteins. 4) We are studying the interaction of interferon with cell membranes.