IFN-γ–dependent nuclear localization of Stat1, Stat1K703R, and Stat1^E705A. Stat1^–/– MEFs expressing physiologic levels of either Stat1 (St1), Stat1^K703R (St1^K703R), or Stat1^E705A (St1^E705A), as in Figure 3, were stimulated with IFN-γ (50 U/mL for 0, 0.5, and 6 hours). Cells were fixed and either imaged for the expression of a GFP reporter gene or after immunostaining with anti-Stat1. Cells were examined under a 40 × Nikon epifluorescence objective. Pictures were taken using a Nikon Plan Fluor ELWD 40×/0.60 objective lens and a SPOT RT color camera with SPOT advanced software (Diagnostic Instruments, Sterling Heights, MI). Data are representative of more than 3 independent studies.