An FRT site flanked neomycin resistance gene cassette and a loxP site were inserted into intron 4. A second loxP site was inserted into intron 8. The neo cassette was removed through subsquent flp-mediated recombination. This leaves a conditional-ready allele with exons 5a through 8 floxed, encompassing all the exons encoding the catalytic domain. (J:240314)