The Emerman laboratory studies the regulatory and structural genes of human immunodeficiency virus (HIV) in order to understand the molecular basis for its pathogenicity. They are interested in understanding the basis for the tropism of HIV in dividing and non-dividing cells, and in host cell defenses against HIV and other retroviruses. Unlike most other retroviruses, HIV can replicate in non-dividing cells such as macrophages. After binding to a cell surface receptor and fusing with the cell membrane, a sub-viral particle reverse transcribes viral RNA into DNA that then integrates into the host genome. With most retroviruses, the cell must pass through mitosis for the viral DNA to enter the nucleus. HIV, however, has evolved to allow nuclear entry independent of the cell cycle; they have found that this is due to characteristics of the capsid protein. Primates have evolved a number of genes that are involved in defense against retroviruses. They are trying to understand the evolutionary pressures on these host genes and the viruses that have shaped human sensitivity or resistance to different infections. They are trying to understand how humans have lost some of the critical factors that could protect against some retroviral infections. A driving force for studies in the lab is the belief that a comparative analysis of the different host and viral requirements for different classes of retroviruses will ultimately underlie the mechanistic basis of the diseases that these viruses cause.