A targeting construct introduced into the locus a floxed neomycin resistance and STOP cassette, the cDNA for a hyperactive version of human Stat3 (A661C and N663C; STAT3C) with a FLAG-tag, and an FRT-flanked IRES-EGFP reporter cassette. In the presence of Cre recombinase, the STOP element is removed and bicistronic expression of STAT3 and GFP occurs. (J:133218)