The targeting construct introduced into the 3'UTR three polyadenylation squences, a RoxP site, a cre recombinase gene and an FRT-flanked neomycin resistance cassette. An additional RoxP site was inserted upstream of the translation start site. Flp-mediated recombination removed the selection cassette. Dre-mediated recombination removed the coding sequence and 3 polyadenylation sequence. (J:215125)