This transgene contains the rat whey acidic protein promoter (0.95 kb of 5' sequence) fused to a mouse Trp53 minigene that carries a transversion in codon 172 (CGC->CTC; "Arg172Leu"). Removal of the ts mutation in the original Trp53 minigene at codon 135 (Ala-Val) and introduction of the Arg-Leu mutation at amino acid 172 were accomplished using recombinant PCR mutagenesis.