A loxP site was inserted upstream of exon 1. An FRT-flanked neo cassette with a 3' loxP site was inserted downstream of exon 1. Flp-mediated recombination removed the neo cassette. Cre-mediated recombination removed exon 1. The absence of protein expression was confirmed by western blot analysis in lung, kidney, heart, spleen, brain, and liver extracts. (J:171715)