A loxP site was inserted upstream of the transcription initiation site. An FRT-flanked neomycin resistance cassette with a 3' loxP site was inserted downstream of exon 2. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exons 1 and 2. Western blot analysis confirmed the absence of protein expression in embryos. (J:235912)