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Effect of Interferon Upon the Primary and Secondary Transcription of Vesicular Stomatitis and Influenza Viruses

The synthesis of viral complementary RNA by vesicular stomatitis virus in permissive cells can be distinguished operationally into two phases, primary transcription, which can be observed in cycloheximide treated cells, and secondary transcription, which represents the further synthesis of viral complementary RNA obtained in untreated cells. Pretreatment of mouse L cells or chicken embryo fibroblasts with the homologous interferon and, for chicken embryo fibroblast cells, poly(rI):poly(rC), inhibits the production of infectious virus and reduces the synthesis of viral complementary RNA to levels comparable to that obtained during primary transcription. Treatment of mouse L cells with interferon plus cycloheximide also gives levels of vesicular stomatitis viral complementary RNA synthesis comparable to that observed with the cycloheximide treatment alone. Similar results have been obtained for interferontreated cells subsequently infected with influenza virus (strain WSN). The results are interpreted as indicating that inhibition of virus development by interferon does not act at the level of primary transcription but rather at an intermediate step between primary and secondary transcription, such as viral protein synthesis.