A LoxP site and an FRT site flanked neomycin resistance gene cassette were inserted into intron 2 and an F3 site flanked puromycin resistance gene cassette and a second loxP site into intron 8. The neo and puro cassettes were removed through subsequent flp-mediated recombination and exons 3-8 were deleted through cre-mediated recombination. Absence of peptide expression from this allele was confirmed by western blots.