IL-3, but not Epo induces the physical association of Jak2 with β_IL3. After starvation, 32D/EpoR-Wt cells were stimulated with various concentrations of IL-3 for 1 minute (A) or for the indicated times with 10 ng/mL IL-3 (B). Cells were lysed in a lysis buffer containing 1% digitonin instead of 1% Triton X-100, immunoprecipitated with anti-β_IL3 , and subjected to anti-Jak2 immunoblotting. The membranes were then reprobed with anti-β_IL3 (C) 32D/EpoR-Wt cells were treated as described in the legend to Fig 1, except that the cells were lysed in the digitonin lysis buffer. The cell lysates were immunoprecipitated with anti-EpoR or anti-β_IL3 , as indicated, and subjected to anti-Jak2 immunoblotting. The membrane was reprobed sequentially with antiphosphotyrosine (αPY), anti-β_IL3 , and anti-EpoR, as indicated. The size markers are indicated and given in kD.