A floxed GFP/hygromycin resistance cassette was placed upstream of exon 3 and an additional loxP site was placed downstream of exon 4. Chimeric mice were bred with Tg(rtetR-TetO-cre)40Mhz mice to remove the selection cassette and leave exons 3 and 4 flanked by loxP sites. Protein expression was unaffected in homozygotes. (J:146210)