ISGF3γ is a nuclear DNA-binding protein. ISGF3 (Interferon Stimulated Gene Factor-3) is the primary transcription activator induced by the binding of interferon α (IFNα) to cell surface receptors. The functional ISGF3 is a complex of four polypeptides of 113 kDa (Stat2), 91 kDa (Stat1α), 84 kDa (Stat1β), and 48 kDa. The first three polypeptides (also known as ISGF3γ) each contain SH2 and SH3 domains. In response to either IFNα, IFNγ, EGF, PDGF, or CSF-1 binding their respective receptors, the cytoplasmic ISGF3α subunits are tyrosine-phosphorylated and translocated to the nucleus where they form an active complex with the 48 kDa protein (ISGF3γ). This complex is responsible for modulating the transcription of interferon-stimulated genes (ISGs). Activated ISGF3α stabilizes ISGF3γ-DNA interactions. This results in a ternary protein-DNA complex with a 25-fold greater stability than ISGF3γ-DNA. Thus, growth factors and cytokines activate a common signal transduction pathway that leads to the phosphorylation and nuclear translocation of a group of latent cytoplasmic transcription factors.