A floxed neomycin resistance cassette was inserted into exon 2. Cre-mediated recombination in ES cells removes the selection cassette prior to insertion of an FRT-flanked neomyin resistance cassette with a 5' loxP site downstream of exon 5. Cre-mediated recombination removed exon 2 through 5. Western blot analysis confirmed the absence of protein expression in the brain. (J:212695)