A loxP site was inserted 5' to exon 3 and a floxed neomycin resistance cassette was placed 3' to the exon. Chimeric male mice were bred to female mice carrying Tg(Tek-cre)12Flv to delete exon 3 and the neomycin resistance gene. This removes the entire GADD45-binding domain and causes a frame shift and premature termination. Absence of protein was confirmed by Western blot analysis.