Activation of M-Ras by IL-3 but not by IL-9. BaF3 cells constitutively expressing the hIL-9 receptor and wild-type M-Ras were cytokine-starved 8 hours in serum-free medium before stimulation with 500 U/mL of either hIL-9 or 3 ng/mL of mIL-3. Thin-layer chromatography of in vivo ³²P-labeled GDP and GTP was perfomed after immunoprecipitation of M-Ras. The result is representative of 3 independent experiments. untreat, untreated cells.