We have examined components of the preintegration complex of human immunodeficiency virus type 1 (H1V-1) and have analyzed features which govern the association of these components. HIV-1 nucleoprotein complexes, isolated from nuclear and cytoplasmic extracts of CD4+ cells after acute virus infection, contained viral RNA and DNA in association with viral matrix (MA), integrase (IN), and reverse ranscriptase (RT) antigens but not capsid (CA) antigens and posessed integration activity in vitro. Association of IN but not RT or MA antigens with viral DNA was detergent-stable. Analysis of viral DNA synthesis and nuclear import of viral nucleoprotein complexes in the presence of a reversible RT inhibitor demonstrated that reverse transcription of viral RNA could be completed entirely in the host cell nucleus. Our studies demonstrate structural and functional features of the nudeoprotein (preintegration) complex of HIV-1 which are pertinent to the understanding of early events in the lentiviral life cycle.

The vpr genes of human and simian immunodeficiency viruses (HIV/SIV) encode proteins which are packaged in the virus particle. HIV‐1 Vpr has been shown to mediate the nuclear import of viral reverse transcription complexes in non‐dividing target cells (e.g. terminally differentiated macrophages), and to alter the cell cycle and proliferation status of the infected host cell. Members of the HIV‐2/SIV(SM) group encode, in addition to Vpr, a related protein called Vpx. Because these two proteins share considerable sequence similarity, it has been assumed that they also exhibit similar functions. Here, we report that the functions of Vpr and Vpx are distinct and non‐redundant, although both proteins are components of the HIV‐2/SIV(SM) virion and reverse transcription complex. Characterizing SIV(SM) proviruses defective in one or both genes, we found that Vpx is both necessary and sufficient for the nuclear import of the viral reverse transcription complex. In contrast, Vpr, but not Vpx, inhibited the progression of infected host cells from the G2 to the M phase of the cell cycle. Thus, two independent functions of the HIV‐1 Vpr protein are encoded by separate genes in HIV‐2/SIV(SM). This segregation is consistent with the conservation of these genes in HIV‐2/SIV(SM) evolution, and underscores the importance of both nuclear transport and cell cycle arrest functions in primate lentivirus biology.

Nuclear import of the retroviral preintegration complex and integration of retroviral with host cell DNA are essential steps for completion of the virus life cycle. The preintegration complex of the lentivirus human immunodeficiency virus type 1 (HIV-1) displays karyophilic properties and, as a consequence, is rapidly directed to the host cell nucleus by an energy-dependent transport pathway. The karyophilic properties of nuclear proteins are governed by a nuclear localization sequence, the targeting function of which can be inhibited in the presence of excess targeting signals. Here we present evidence that the nuclear import of a large karyophile-the preintegration complex of HIV-1-is inhibited in the presence of a prototypic nuclear targeting signal of simian virus 40 T antigen. This points to a novel strategy which prevents establishment of the provirus by interrupting nuclear localization of HIV-1 DNA.

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