TYROSINE-PHOSPHORYLATED STAT1 AND STAT2 PLUS A 48-KDA PROTEIN ALL CONTACT DNA IN FORMING INTERFERON-STIMULATED-GENE FACTOR-3

Interferon a induction of transcription operates through interferon-st imulated-gene factor 3 (ISGF), a transcription factor two components o f which are members of the newly characterized Stat family of transcri ption factors. Interferon alpha induces tyrosine phosphorylation of St at1 and Stat2 proteins that associate and, together with a 48-kDa prot ein, form ISGF3, Evidence is presented that a heterodimer of Stat1 and Stat2 is present in ISGF3 and that Stat1 and the 48-kDa protein make precise contact, while Stat2 makes general contact, with the interfero n-stimulated response element, the binding site of the ISGF3.