An frt flanked neomycin cassette with a 5' attached loxP site was inserted in intron 3. An additional loxP site was inserted in intron 1. Exons 2 and 3 of the resulting allele are thus flanked by loxP sites. Mice were crossed to transgenic mice carrying a beta actin-cre to excise exons 2 and 3. This results in a frameshift mutation creating a stop site at codon 16. The resulting mice retain the frt flanked neomycin resistance cassette.