Hypersensitivity of BaF3 cells expressing an Epo-R unable to bind β-Trcp. Three independent BaF3 clones expressing Epo-R^WT and 3 independent BaF3 clones expressing Epo-R^S462A were tested for Epo sensitivity by ³H-thymidine incorporation. Cells were grown 3 days with the indicated concentration of Epo before measuring ³H-thymidine incorporation. Inset shows the results of a typical experiment. Each cell clone was tested in 3 independent experiments. To allow comparison between experiments, maximum ³H-thymidine incorporation, which was always obtained in incubations with 10 U/mL Epo, was set at 100 for each cell line in each experiment and ³H-thymidine incorporation observed using lower Epo concentrations was expressed relative to this value. The main graph depicts the results of the 9 determinations and error bars represent standard deviations. The asterisk indicates a P value < 0.05 by Student t.