A targeting vector was designed such that the codons of the five C-terminal amino acids, VWRPY, were changed to the stop codon UAG and to codons encoding substituted amino acids designed to create a new NotI site. A loxP-flanked neo was included in intron 5 and was subsequently removed via cre-mediated excision. RT-PCR and Western blot analyses demonstrated expression of the mutant transcript and protein, respectively.