The transgene consists of a 4.5 kb genomic fragment of the mouse whey acidic protein promoter (Wap) followed by a rabbit beta-globin intron, cre coding sequence, and a transcription termination/polyadenylation fragment from the human growth hormone gene. The purified 7.8 kb fragment was microinjected into one-cell stage embryos from FVB/N mice. This is a high expressing line (51).