DESCRIPTION: This application proposes to identify the mechanism(s) by which Nef accentuates the infectivity of HIV particles. To determine if Nef interferes with uncoating, preintegration complexes will be purified and analyzed for their viral protein compositions, and the sensitivity of the viral genome to RNase A will be assessed. In addition, an in vitro assay for uncoating, utilizing detergents or cytoplasmic lysates, will be developed, and nef-defective virions will be tested for altered behavior. Finally, protein composition and RNA structure of wild-type and nef-deleted virions will be determined using a combination of biochemical assays, and virion structure assessed before and after entry into target cells using electron microscopy. It is hoped that these studies will elucidate the mechanism(s) by which Nef increases particle infectivity and add insights into new therapeutic opportunities.