ASSOCIATION OF HUMAN-IMMUNODEFICIENCY-VIRUS NEF PROTEIN WITH ACTIN ISMYRISTOYLATION DEPENDENT AND INFLUENCES ITS SUBCELLULAR-LOCALIZATION

Human immunodeficiency virus (HIV) Nef functions are thought to be med iated via interactions with cellular proteins. Utilizing zone velocity sedimentation in glycerol gradients we found that recombinant HIV-1 N ef non-covalently associates with actin forming a high-molecular-mass complex of 150-300 kDa. This Nef/actin complex was present in human B and T lymphocytes but not in insect cells and was dependent on the N-t erminal myristoylation of Nef, whereas the SH3-binding proline motif o f Nef was not involved. Despite being myristoylated, HIV-2 Nef did not associate with actin. This might reflect differences in the subcellul ar localization of Nef since cell-fractionation experiments revealed t hat HIV-1 Nef was virtually exclusively localized in the cytoskeletal (detergent-insoluble) fraction whereas HIV-2 Nef heel significantly re duced affinity for the cytoskeleton. Colocalization experiments in HIV -1-infected CD4+ fibroblasts revealed that Nef/actin complexes may als o exist in HIV-infected cells. This novel interaction of HIV-1 Nef wit h actin provides insight into the association of Nef with cellular str uctures and reveals general differences in the interactions of the Nef proteins from HIV-1 and HIV-2.