Jak1 is responsible for partial signaling of Jak2-FF within the IFNGR complex. (A) Jak2^+/+, Jak2^FF/FF, Jak2^−/−, and Jak1^−/− MEFs were stimulated with IFN-γ for the indicated time points. Subsequently, cellular lysates were prepared and analyzed by immunoblotting for expression of phospho-Jak1 (Y1022/1023) and Jak1 protein. β-actin served as a loading control. Results shown are representative of 3 independent experiments. (B) Jak2^+/+, Jak2^FF/FF, and Jak2^−/− MEFs stably expressing either a scrambled small hairpin RNA (shRNA) (mock) or shRNAs directed against 2 different target sequences of Jak1 (shRNA 1, shRNA 2) were stimulated for the indicated times with IFN-γ. Cellular lysates were prepared and analyzed by immunoblotting for expression of phospho-Stat1 (Y701). To verify the knockdown, cellular lysates were analyzed for Jak1 protein expression. β-actin served as a loading control. (C) Jak2^+/+, Jak2^FF/FF, Jak2^−/− and Jak1^−/− MEFs were stimulated with IFN-γ for the indicated time points. Cellular lysates were prepared and immunoprecipitation (IP) with an antibody against IFNGR1 was performed. Subsequently, the indicated proteins were analysed by immunoblotting.