A loxP site was inserted 5' to exon 2, and a loxP- and FRT-flanked neomycin cassette was placed 3' to exon 4. The FRT-flanked neomcycin cassette was deleted by crossing the mice with a widely-expressed Flp strain. To create this allele (delta P), the floxed exons were also excised by crossing to a widely expressing Cre strain, leaving a single loxP site. (J:237954)