A loxP site was inserted at an SpeI site 384 bp 3' of the third coding exon, in intron 3. A second loxP together with a Frt-PGK-neo-Frt selection cassette site was inserted at a StuI site 279 bp 5' of the exon, in intron 2. Flp-mediated recombination removed the neo cassette and left exon 3 floxed. (J:228792)