Activation of transcription factors by interferon-alpha in a cell-free system.

The signal transduction mechanisms of interferons (IFNs) remain unclear partly because no effect of IFN has been reproducible in a cell-free system. IFN-alpha rapidly induces the transcription of a set of early response genes, and a multicomponent transcriptional activator, interferon stimulated gene factor 3 (ISGF3), is activated within minutes after binding of IFN-alpha to its receptor. A system was developed in which IFN-alpha activated ISGF3 in homogenates of HeLa cells. Subcellular fractionation revealed that incubation of a plasma membrane-enriched fraction with IFN-alpha was sufficient to activate the regulatory subcomponent of ISGF3.