Activation of SAPKγ by hematopoietic growth factors. MC/9 cells were incubated at 37°C in RPMI 1640 for 1 hour and then left untreated (CON), or treated with saturating doses of IL-3 (IL-3), IL-4 (IL-4), GM-CSF (GM), SLF (SLF ), or 0.2 mol/L NaCl (NaCl) for the indicated times. Immunoprecipitated SAPKγ was analyzed using an in-gel kinase assay after SDS-PAGE with a separating gel containing GST-c-jun. The phosphorylation of c-Jun was assessed by autoradiography and the presence of 46- and 55-kD splice variants of SAPKγ are indicated.