A loxP site was inserted upstream of exon 2. An FRT- and loxP-flanked neomycin resistance cassette was inserted downstream of exon 2. Flp-mediated recombination removed the neomycin resistance cassette and left exon 2 floxed. Cre-mediated recombination removed exon 2. Western blot analysis confirmed the absence of protein expression in embryos. (J:199325)