PI 3-kinase associates with several tyrosine-phosphorylated proteins in Epo-stimulated cells. UT-7 cells were serum- and growth factor-starved for 18 hours and incubated for 10 minutes in the presence (+) or absence (−) of 10 U/mL Epo. The cells were then lysed using 1% Brij 98 and the lysates were cleared by centrifugation (27000g for 15 minutes). Lysates from 10⁷ cells were immunoprecipitated using anti–PI 3-kinase antibodies. Immunoprecipitates were analyzed by Western blot using antiphosphotyrosine antibodies (anti-PY) and anti–PI 3-kinase (anti–PI3-K) antibodies, successively.