Immunoblotting of IRF-1 (A), IRF-2 (B), and Stat1 (C; upper portion) protein in retrovirus transfected KG1a cells with or without IFN-γ stimulation. (C; lower portion) Cell lysates were immunoprecipitated by antiphosphotyrosine MoAb (4G10) and then immunoblotted by anti-Stat1α antibody.