Site-directed mutagenesis was performed to substitute methionine 318 with arginine (ATG->CGG; adenine to cytosine, and thymine to guanine at nucleotides 952 and 953 respectively) in exon 5 of the targeted gene. A loxP-flanked neomycin selection cassette was placed in intron 6. Cre-mediated recombination removed the floxed neo cassette. (J:204960)