Induction of STAT1β and STAT1α. (A) Schematic diagram of the CKR516-STAT1β vector. Gray boxes indicate cassettes; BI-tet07, bidirectional tetracycline-responsive promoter; STAT1β, cDNA encoding STAT1β; EGFP, cDNA encoding the enhanced green fluorescence protein; rtTA, reverse tetracycline-repressor transactivator fusion protein rtTA2^s-M2; EBV oriP, origin of replication of the EBV plasmid; HygR, gene for hygromycin resistance; Eμ-RSV, promoter-enhancer consisting of mouse immunoglobulin heavy chain intron enhancer and RSV promoter; and SfiI, restriction sites for SfiI. (B) Expression of STAT1β and STAT1α in LCL cells transfected with CKR516-STAT1β and CKR516-STAT1α. STAT1β and STAT1α expression was assessed after 4 weeks of selection by hygromycin using Western blotting with an anti-STAT1 antibody recognizing STAT1α (91 kDa) and STAT1β (84 kDa), as indicated by arrows. Analysis was performed in transfected cells that were either treated (+) or not treated (–) with 1.5 μg/mL doxycycline for 24 hours. This experiment is representative of 4 independent transfections of cells. In each case, the percentage of EGFP-inducible cells was approximately 70%.