IFN-–induced tyrosine phosphorylation of JAK1, Tyk2, and STAT1 in Daudi and its IFN-resistant clone. Parental Daudi cells (Daudi) or IFN-resistant cells (Daudi^R) were stimulated with IFN- (1,000 IU/mL) for 15 minutes and lysed. The postnuclear supernatants were immunoprecipitated with anti-JAK1 (A) or anti-Tyk2 (B). The immunoprecipitates were blotted with antiphosphotyrosine antibody (upper panels), then the membrane was stripped and reprobed with anti-JAK1 (A) or anti-Tyk2 (B) antibodies (lower panels). (C) Total cell extracts were also blotted with anti-phospho STAT1 (PY-STAT1) and anti-STAT1 (STAT1).