A targeting vector was designed to introduce a GGA to CGA mutation in exon 9, resulting in a glycine to arginine substitution at position 418 (G418R), and a floxed neomycin resistance cassette. The floxed neomycin resistance cassette was removed via cre-mediated recombination. The murine G418R mutation is analogous to the G420R mutation frequently seen in human cherubic patients. (J:221901)