Superantigen Expression Is Driven by Both Mouse Mammary Tumor Virus Long Terminal Repeat-Associated Promoters in Transgenic Mice

In addition to the usual retroviral promoter, the mouse mammary tumor virus (MMTV) long terminal repeat carries a second promoter located in the U3 region. Here we show that both of these promoters are independently able to give rise to superantigen activity in transgenic mice. The ability of multiple MMTV promoters to drive superantigen expression underscores its importance in the virus life cycle.