Central to the replication of HIV-1 is the precursor Gag polypeptide (p55) which is able to direct the assembly and release of virion-like particles even in the absence of all other virus encoded components. The p55 thus contains all of the necessary signals involved in directing its intracellular transport from its site of synthesis in the cytoplasm to the plasma membrane where virus formation and budding occurs. Evidence indicates that this intracellular assembly is a multi-step process controlled by several unique Gag structural domains. We have used subcellular fractionation of cells expressing Gag mutant proteins to identify structural features involved in p55 intracellular transport, membrane binding, and/or function. One of these predicts an amphipathic alpha-helix within the capsid domain which appears to be required for membrane localization and viral budding. Others include the co- translational N-myristoylation by the host N-myristoyltransferase and post-translational phosphorylation by protein kinase C which appear to be required for the membrane association of the mature Gag matrix protein (p17). The role of these domains in regulating the interaction of Gag proteins with specific subcellular components (e.g., cytoskeleton, plasma membrane) is being investigated. The detailed regulatory mechanisms responsible for each signal is being examined and the possible susceptibility of each process to chemotherapeutic intervention is being examined.
