Constitutive and ligand-induced transcriptional activation by Δ5TpoR. Ba/F3 cells selected in Tpo or without cytokines were starved for 3 hours in RPMI/1mg/mL BSA and electroporated with pGL3bPpr2-luc, pLHRE-luc, or pSRE-luc in order to measure transcriptional activity of STAT3 (A), STAT5 (B), or MAP kinase (C), respectively. pRL-TK encoding the renilla luciferase was coelectroporated for normalization of luciferase values. Cells were stimulated with 50 ng/mL Tpo or mock-treated as indicated. Cell lysates were prepared 2 hours after stimulation and analyzed for luciferase activity. Results shown here reflect averages of triplicate values ± SD. Similar results were obtained performing 3 independent experiments.