A targeting vector was designed to insert a loxP site upstream of exon 2, and an FRT-splice donor/acceptor-IRES-beta-gal/neo-FRT-loxP downstream of exon 3. ES cells were transiently transfected with a FLP-expressing plasmid to remove the SA-IRES-betageo cassette leaving exons 2-3 floxed. (J:234617)