The 34-bp loxP sequence with 26-bp linker sequence was inserted into the site 210 bp upstream of exon 2. A 1.8 kb DNA fragment, which carried the 34 bp loxP sequence and Pgk-1 promoter-driven neomycin phosphotransferase gene (neo) flanked by two Flp recognition target (frt) sites was then inserted into the site 190 bp downstream of exon 3. (J:302794)