In human prostate cancer, the first exon of TMPRSS2 is entirely within the non-coding 5’ UTR and most TMPRSS2-ERG fusions involve the first intron of TMPRSS2, with the resulting fusion transcript containing no coding sequence of TMPRSS2. We therefore replaced exon 2 with a cassette including an adenovirus splice acceptor (SA), followed by a PGK-driven neomycin selection cassette flanked by FRT recombination sites, followed by the CreERT2-IRES-nlsGFP. The gene discussed is TMPRSS2; the disease is prostate cancer.