This transgene contains the MMTV (mouse mammary tumor virus) promoter and a 4.6 kb cDNA from the rat Erbb2 (avian erythroblastosis B2) oncogene. The activated form of the gene is used in this construct, which differs from the wild-type allele by a point mutation, Val664Glu. Six transgenic lines were produced (NA, NB, NF, NK, NL and NM).