Comparison between EGFP and STAT1β induction. (A) Dose-response induction of EGFP. The expression of EGFP was analyzed in nontransfected PRI cells (PRI) and in CKR516-STAT1β–transfected cells after 4 weeks of selection by hygromycin. Autofluorescence of nontransfected PRI cells was lower than that of CKR516-STAT1β–transfected cells and did not change with doxycycline treatment. CKR516-STAT1β–transfected cells positive for EGFP after 24 hours of treatment with 0 to 0.6 μg/mL doxycycline were detected by flow cytometry in the G area on an FL1/side-scatter dot plot. The concentration of doxycycline is indicated above each graph. The percentage of EGFP-positive cells is indicated under each graph. (B) Dose-response induction of STAT1β. Western blot analysis was performed as for Figure 1. Analysis was performed in the same cells in panel A, with EGFP induction ranging from 2% to 77%. Arrows indicate the correspondence between the EGFP flow cytometry dot plot and the different lanes of the Western blot. Results are representative of 2 different experiments. Comparable results were obtained with CKR516STAT1α–transfected cells.