A targeting vector was designed to insert a loxP- and FRT-flanked neomycin resistance (neo) cassette upstream of exon 5, and a second loxP site downstream of exon 8. FLPe-mediated recombination removed the FRT-flanked cassette leaving exons 5 through 8 floxed. Cre-mediated recombination removed exons 5 through 8. Exons 5 through 8 encode a substantial portion of the catalytic domain of the gene. (J:213412)