RMCE on KH2 cells inserted a cassette, which contained a tetracycline response element driving doxycycline-inducible expression of the human cDNA with nucleotide substitutions that result in the amino acid substitution of alanine for serine at position 127 (S127A), into the 3'UTR. This mutation produces a protein with increased nuclear localization and transcriptional activity compared with the wild-type protein.