A targeting vector designed to replace sequence encoding 117 carboxy terminal amino acids with sequence encoding EGFP and neo was inserted at the endogenous locus via homologous recombination. RT-PCR and Northern blot analyses confirmed the presence of fusion transcript in mutant mice. Western blot analysis showed the level of fusion protein to be approximately half of that of the wild-type protein, indicating reduced stability. GFP fluorescence was not detected in mutant mice.