Signal Transducer and Activator of Transcription 6 (STAT6) is a member of the Jak/STAT signal transduction pathway and mediates cytokine signaling by IL-4. IL-4 activation leads to tyrosine phosphorylation and accumulation in the nucleus of STAT6 homo and heterodimers. STAT6 acts as a signal transducer in the cytoplasm and, upon phosphorylation at Y641, translocates to the nucleus and binds to the DNA consensus site TTCN4GAA. Knockout studies in mice suggest that STAT6 functions in differentiation of T helper 2 (Th2) cells, expression of cell surface markers, and class switch of immunoglobulins. STAT6 transcriptional activation occurs by binding p100 and p160 class (NcoA1, Src-1) co-activators. Gene expression studies indicate that STAT6 mediates cell proliferation and anti-apoptotic effects of IL-4.