A floxed corresponding cDNA with a polyadenylation sequence was inserted upstream of exon 16. An IRES, lacZ and polyadenylation sequence followed by an FRT-flanked neomycin resistance cassette replaced exon 17. Flp-mediated recombination removed the neomycin resistance cassette. Cre-mediated recombination removed the cDNA. Western blot analysis confirmed the absence of protein expression in E18 embryos. (J:203073)