Using a targeting vector constructed with C57BL/6 BAC genomic clone, a floxed neo cassette was inserted upstream of exon 5 and an additional lox P site was inserted downstream of exon 7. Cre-mediated recombinated removed the neo cassette and exons 5 through 7 to create a truncated protein detectable by western blot analysis that lacks a complete PDZ dmain and leucine zipper.