DESCRIPTION (adapted from Abstract): The human immunodeficiency virus, Type 1 (HIV) is a type C retrovirus that assembles at the plasma membrane. Like other retroviruses, only gag proteins are required for proper assembly, although other components are required for virus infectivity. In the proposed project the Principal Investigator and his associates will examine the cis and trans determinants of the HIV assembly pathway and will ask whether this information can be exploited in the development of trans-dominant inhibitors of particle formation. Their major focus in this study is on determinants required for gag interactions with membranes, and determinants required for the assembly at the plasma membrane rather than intracellular sites. They will use a combination of mutational analysis, recombinant vaccinia virus and HIV expression systems, cell-fractionation assays, and electron microscopy to decipher the assembly pathway. In Specific Aim #1 the researchers will assess the membrane association determinants of gag, utilizing cell-free systems with Escherichia coli and reticulocyte lysate expressed gag proteins to define further the component(s) at the membrane that interacts with gag. In the Specific Aim #2, the researchers will examine the sites of gag phosphorylation and their roles in virus assembly, utilizing biochemical and genetic approaches. In Specific Aim #3 the researchers will examine trans determinants of virus assembly, in particular the regulatory proteins, Vif and Vpu, utilizing the vaccinia virus expression system, to explore the way Vif alters viral nucleocapsid packing which is critical for virus infectivity. Also, the researchers will utilize the vaccinia virus expression system to explore the way Vpu enhances virus particle release. In each case, they will examine the effects on membrane interactions and the structure and expression of extracellular virions, as well as identify the domains in Pr55gag that are critical for regulation by Vif or Vpu.