All reactions, whether transgene-positive or not, amplified a segment of the endogenous prion protein gene as a control for DNA quality using a forward primer, PrP-S-J, specific to the mouse PrP open reading frame (GGG ACT ATG TGG ACT GAT GTC GG) and a reverse primer, PrP-AS-J, shared by the 3′ UTR of the endogenous PrP gene and the transgene vector.