Ihh^tm2Amc

Frt-flanked neo-tk cassette with a loxP site was introduced into the first intron and another loxP site was introduced into the 5' leader sequence of the first exon by homologous recombination. The neo-tk cassette was excised by transient transfection of properly targeted ES cells with a flpe-expressing plasmid, leaving exon 1 flanked by loxP sites. (J:99641)