The targeting vector is designed to insert a loxP site in intron 1, an FRT-flanked self-excising FLPe/neo cassette (frt::Prm1-FLPe-SV40pA::Pol2-neo-SV40pA::frt) in intron 2, and a second loxP site in intron 3 of the the gene. The neo cassette was deleted by transiently transfection of an expression vector of flp recombinase in the ES cells. (J:101977)