A loxP site was inserted upstream of exon 2 and an FRT flanked neo cassette and loxP site were inserted downstream of exon 3 via homologous recombination. Recombinase mediated recombination removed the neo cassette and exons 2 and 3. Western blot analysis confirmed the absence of protein expression in testis and epididymis lysates from homozygous mice. (J:307371)