Inhibition of IFN-β– and IFN-γ–induced JAK activation by JAB. NIH3T3 parental cells (parent) and JAB transformants (JAB) were stimulated with 1,000 IU/mL IFN-γ (A and B) or IFN-β (C and D) for 15 minutes and lysed. The postnuclear supernatant was immunoprecipitated with anti-JAK1 (A and C) anti-JAK2 (B), or anti-Tyk2 (D). The immunoprecipitates were blotted with antiphosphotyrosine antibody (upper panels), then the membrane was stripped and reprobed with anti-JAK1 (A and C), anti-JAK2 (B), or anti-Tyk2 (C) antibodies (lower panels).