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, leaving a conditional-ready allele with exons 3-8 floxed. (J:306481)