Exon 2 was modified to encode 5 amino acid substitutions: T232D, K251A, K254S, K255A, K256A. This also creates an additional NheI restriction site. A floxed neomycin selection cassette was inserted in intron 1. The floxed neo was subsequently excised by crossing to Tg(CMV-cre)1Cgn. Western blot analysis indicates that expression is somewhat reduced and the protein is somewhat insensitive to RAS.