Tyrosine phosphorylation of IFN-α–signaling elements in cells lacking expression of IRS-proteins. Antiphosphotyrosine immunoblots are shown. (A) 32D^IR cells were incubated for 5 minutes at 37°C in the presence or absence of mouse IFNα/β as indicated, and cell lysates were immunoprecipitated with either an antibody against Tyk-2 (Santa Cruz) or nonimmune RIgG as indicated. (B) 32D cells were incubated for 5 minutes at 37°C in the presence or absence of mouse IFNα/β as indicated, and cell lysates were immunoprecipitated with an antibody against Jak-1 as indicated. (C) 32D cells were incubated for 5 minutes at 37°C in the presence or absence of mouse IFNα/β as indicated, and cell lysates were immunoprecipitated with an antibody against Vav as indicated. (D) 32D cells were incubated for 20 minutes at 37°C in the presence or absence or presence of mouse IFNα/β as indicated, and cell lysates were immunoprecipitated with either an antibody against Stat-1 (Santa Cruz) or nonimmune RIgG as indicated.