A loxP site flanked puromycin resistance gene/transcription stop cassette was inserted into intron 1 and mutations were created in exon 2 altering codon 25 from leucine to glutamine (p.L25Q) and codon 26 from tryptophan to serine (p.W26S). Further changes in exon 4 altered codon 53 from phenylalanine to glutamine (p.F53Q) and codon 54 from phenylalanine to serine (p.F54S). Both transactivation domains are incapacitated once the stop sequences are removed by cre expression. (J:173395)