Interferon-stimulated response element (ISRE)-binding protein complex DRAF1 is activated in sindbis virus (HR)-infected cells

To elucidate the host cell defense mechanisms in response to Sindbis viral infection, we have started to characterize interferon (IFN)-stimulated resp onse element (ISR-E)-binding proteins activated in infected cells that are involved in the transcriptional induction of IFN type I-inducible genes. Us ing electromobility shift assays (EMSA), we detected several protein comple xes with a human IFN-stimulated gene 15 (ISG15) ISRE in extracts from virus -infected L929 cells that were absent in extracts from uninfected cells. Co migration with Newcastle disease virus-activated ISRE-binding complexes, IS RE-binding specificity, supershift experiments, and conditions of formation indicate that the complexes activated by Sindbis viral infection in L929 c ells correspond to DRAF1 and ISG factor 3 (ISGF3). Transfection of L929 cel ls with poly rI:rC induced only ISGF3. DRAF1 could be detected in Sindbis v irus-infected mouse embryo fibroblasts derived from IFNR type I and type II KO mice. Viral RNA synthesis is required for activation of DRAF1.