A loxP site was inserted 42 bp upstream of the lone coding exon and a Frt-flanked neomycin cassette, another loxP site, and a myc-tagged luciferase coding sequence were inserted downstream of the exon in the BstAPI restriction site. After targeting in BALB/c ES cells, the neomycin cassette was removed by transient expression of Flp recombinase. (J:151854)