Thirty bp (codons for 10 amino acids) in exon 3 were replaced with a floxed cassette composed of a neomycin resistance gene and cre placed under the direction of a testis specific angiotensin converting enzyme pomoter. Cre expression in the germline of chimeric male mice excised the inserted cassette leaving a deletion in exon 3 including two of three zinc binding histidine residues and introducing a frameshift beginning in exon 4. A stop codon was created after 11 missence amino acids.