Our research interests revolve around obtaining a better understanding of the interaction of retroviruses with their host cells and organisms. We use simple retroviruses (avian and murine viruses) as well as HIV to elucidate the nature of the retrovirus-receptor interaction; control of viral gene expression; mechanism of retroviral genetic variation; and evolution of the host-virus relationship, as revealed by the fossil record provided by endogenous proviruses found in the normal DNA of all vertebrates and many other species.