The targeting vector is designed to replace the entire coding region of the gene with an enhanced green fluorescent protein (EGFP) sequence. An FRT-flanked neomycin resistance (neo) cassette with a polyadenylation signal (polyA) in reverse orientation to the gene were inserted into the 3' UTR. FLP-mediated recombination removed the FRT-flanked neo cassette. Immunoblot analysis confirmed the absence of protein expression in various tissues of homozygous mutant mice.