A loxP site was inserted upstream of exon 1. An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted downstream of exon 3. Flp-mediated recombination removed the neomycin resistance cassette. Cre-mediated recombination removed exons 1-3 containing the coding sequence. Western blot analysis confirmed the absence of protein expression in ES cells and testis. (J:198685)