Site-directed mutagenesis was performed to substitute glycine 358 with tryptophan (GGC->TGG; guanine to thymine and cytosine to guanine at nucleotides 1069 and 1071 respectively) in exon 4 of the targeted gene. A loxP-flanked neomycin selection cassette was placed in intron 3. Cre-mediated recombination removed the floxed neo cassette.