HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 VPR LOCALIZATION - NUCLEAR TRANSPORT OF A VIRAL PROTEIN MODULATED BY A PUTATIVE AMPHIPATHIC HELICAL STRUCTURE AND ITS RELEVANCE TO BIOLOGICAL-ACTIVITY

Protein import into the nucleus is generally considered to involve spe cific nuclear localization signals (NLS) though it is becoming increas ingly clear that efficient and well controlled import of proteins whic h lack a canonical NLS also occurs in cells. Human immunodeficiency vi rus type 1 (HIV-1) Vpr is one such protein which does not have an iden tifiable canonical NLS and yet efficiently localizes to the nuclear co mpartment. Here, we use confocal microscopy to demonstrate that mutati ons in the putative central hydrophobic helix of Vpr result in the ret ention of the protein in highly localized ring-like structures around the nuclear periphery with striking impairment in their ability to ent er the nuclear interior. By characterizing other biological activities associated with this protein, such as its ability to incorporate into budding virions and its ability to arrest cells in G2, we show that t his helical domain is specific for the nuclear translocation of the pr otein with very little effect on these other functions. interestingly, however, perturbation of this helical motif also perturbs the protein 's ability to augment viral replication in primary human macrophages i ndicating that the integrity of this secondary structure is essential for optimal infection in these non-dividing cells. (C) 1998 Academic P ress Limited.