Interferon and growth factor modulation of nuclear factors binding to 5′ upstream elements of the 2–5A synthetase gene

We assayed fragments of the 5′ flanking sequence of the human 2–5A synthetase gene for their ability to respond to interferon‐α (IFN) and platelet‐derived growth factor (PDGF). Transient transfection assays identified a 40‐base pair fragment, which, regardless of orientation, could confer IFN‐inducibility on the thymidine kinase promoter. This same fragment was active in monkey and mouse cells and in the latter was responsive to PDGF. The effect of PDGF could be inhibited by anti‐interferon antibodies. Gel retardation assays, using the 40‐base pair probe, detected the presence of IFN‐modulated DNA‐binding factors in nuclear extracts from monkey cells. In mouse cells both IFN and PDGF induced the binding of nuclear factors to a synthetic 2–5A synthetase response sequence. Thus, both IFN and growth factors directly or indirectly modulate the binding of nuclear factors to the same region of the 2–5A synthetase gene.