The endogenous locus was targeted with two rounds of homologous recombination that inserted a floxed neomycin selection cassette into intron 2 and a cassette containing a floxed puromycin resistance gene followed by lacZ into the 3' untranslated region. Exons 3 through 17 were flanked by the floxed selection genes. The production of transcript and protein from this allele was verified by Northern and Western blot analyses. (J:78711)