A lox5171 site was inserted upstream of exon 1. An F3 site flanked hygromycin resistance cassette with a 5' lox5171 site was inserted downstream of exon 3. The construct was injected into ES cells containing the Tex19.1tm2Ics allele. Flp-mediated recombination removed the hygro 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)