An FRT flanked neomycin/kanamycin selection cassette and loxP site were inserted upstream of exon 4 and a loxP site was inserted downstream of exon 6 via homologous recombination. Cre mediated recombination deleted exons 4 - 6. RT-PCR and western blot analysis confirmed the absence of wild-type RNA and protein expression in testes and MEFs, respectively, from homozygous mice. RT-PCR analysis did detect expression of a small transcript containing exons 7 and 9 in testes from homozygous mice.