A targeting vector was designed to insert a single loxP site approximately 1 kb and amino acids 1-50 upstream of exon 1, and an FRT-flanked neomycin resistance (neo) cassette, followed by a second loxP site, downstream of exon 1 of the gene. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exon 1 floxed. (J:234692)