Fig. 3. The EgΔBY440 receptor mediates an IFN-γ-like transcriptional response (A) that is dependent on STAT1 (B). Wild-type 2fTGH (2f) or STAT1-negative U3A cells, stably transfected with the chimeric receptor as indicated, were stimulated for 6 or 18 h (A) or for 18 h (B) with 500 IU/ml IFN-γ and/or 100 U/ml Epo. Aliquots (13 µg) of cytoplasmic RNA were analysed for inducible gene expression by RNase protection assay using 9-27, IRF-1, 6-16 and Class II HLA DRA as probes, with γ-actin as a loading control (Materials and methods). In parallel EMSA controls, comparable activation of STAT1 was observed in response to Epo in the 2f/Eg and 2f/EgΔBY440 cells.