A loxP site was inserted upstream of exon 1 and a FRT-flanked PGK-neomycin resistance cassette and a second loxP site were inserted downstream of exon 1. Flp-mediated recombination removed the neomycin resistance cassette and cre-mediated recombination deleted exon 1. Western blot analysis confirmed absence of protein in brain, skeletal muscle, small intestine, liver, heart, and kidney. (J:270551)