A loxP site was inserted upstream of exon 1. A Loxp and FRT site flanked neomycin resistance gene cassette with a 5' loxP site was inserted downstream of exon 3. Flp-mediated recombination removed the neo 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:243444)