A targeting vector was designed with 3 loxP sites such that exon 5 and a PGK-neo could either both or either be removed from the locus by cre expression. Removal of exon 5 would result in a frame shift that would putatively produce a nonfunctional 244 amino acid product with a molecular weight of 26.8 kDa instead of the ~130 kDa wild-type protein.