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PubMed2003

Quantitative analysis of human immunodeficiency virus type 1 DNA dynamics by real-time PCR: integration efficiency in stimulated and unstimulated peripheral blood mononuclear cells.

We established a set of real-time PCR assay to accurately quantify human immunodeficiency virus type 1 (HIV-1) DNA in infected cells. Using this assay we were able to measure the strong-stop, full-length/ 1-LTR circle, 2-LTR circle, and integrated forms of viral DNA, and the data provided was quite consistent with the characteristics of mutant viruses in early phase of infection. Since our assay is particularly applicable to quantify the integrated DNA in small scale of samples, we measured the level of integrated DNA in wild-type virus (WT)- or Vpr-defective virus (deltaVpr)-infected peripheral blood mononuclear cells (PBMC), and examined whether quiescent condition of the PBMC influences integration step of HIV-1. Under stimulating condition approximately 25% of total viral DNA was in integrated form in either WT- or DeltaVpr-infected cells. In contrast, under unstimulated condition the level of integration efficiency was not significantly reduced in WT-infected cells, while this efficiency was severely impaired in the absence of vpr gene. This result clearly demonstrated a crucial role of the Vpr for nuclear localization and subsequent integration of viral DNA in nondividing cells. Therefore, our assay is useful for analyzing the events in early phase of HIV-1 infection under various conditions.

Cell Culture Techniques↗
PubMed2000

Induction of cell-cycle arrest in cervical cancer cells by the human immunodeficiency virus type 1 viral protein R.

OBJECTIVE: To determine the ability of the human immunodeficiency virus type 1 (HIV-1) gene vpr to induce cell-cycle arrest in cervical cancer cells with or without human papillomavirus (HPV) type 16 E6 or E7 expression. METHODS: High- and low-level expression vectors for vpr (designated pVPR(HIGH) and pVPR(LOW), respectively) were used in conjunction with HPV-16 E6 or E7 vectors to transfect HPV-negative C33A cervical cancer cells. Vpr expression vectors encode a cell surface marker gene, murine Thy-1, for specific detection of transfected cells. Dual staining for the surface molecule Thy-1 and DNA content was used to determine cell-cycle profile and G2-phase arrest. RESULTS: C33A cells not expressing HPV-16 E6 showed some but not maximal G2-phase arrest when transfected with pVPR(HIGH) alone (43.2% of cells in the G2 phase). Addition of HPV-16 E6 or E6 plus E7 to pVPR(HIGH) substantially increased the percentages of cells in the G2 phase (51.3% and 53.0%, respectively). Cotransfection with pVPR(HIGH) and HPV-16 E7 did not increase significantly the percentage of cells in the G2 phase compared with pVPR(HIGH) alone (40.6% versus 43.2%). In transfections involving pVPR(LOW), a slight degree of G2-phase arrest was observed when Vpr was expressed alone (29.0% of cells in the G2 phase) or in cotransfection with HPV-16 E7 (33.2% of cells), and G2-phase arrest was augmented with the addition of HPV-16 E6 (41.7%) or E6 plus E7 (45.7%). CONCLUSION: Cervical cancer cells are susceptible to cell-cycle arrest induced by HIV-1 vpr. This effect is exacerbated by coexpression of HPV-16 E6, although E6 alone is incapable of inducing any detectable G2-phase arrest, suggesting that E6 and VPR share links in cell-cycle signaling pathways.

Cell Cycle↗
PubMed1998

Virion-targeted viral inactivation of human immunodeficiency virus type 1 by using Vpr fusion proteins.

Inactivation of progeny virions with chimeric virion-associated proteins represents a novel therapeutic approach against human immunodeficiency virus (HIV) replication. The HIV type 1 (HIV-1) Vpr gene product, which is packaged into virions, is an attractive candidate for such a strategy. In this study, we developed Vpr-based fusion proteins that could be specifically targeted into mature HIV-1 virions to affect their structural organization and/or functional integrity. Two Vpr fusion proteins were constructed by fusing to the first 88 amino acids of HIV-1 Vpr the chloramphenicol acetyltransferase enzyme (VprCAT) or the last 18 C-terminal amino acids of the HIV-1 Vpu protein (VprIE). These Vpr fusion proteins were initially designed to quantify their efficiency of incorporation into HIV-1 virions when produced in cis from the provirus. Subsequently, CD4+ Jurkat T-cell lines constitutively expressing the VprCAT or the VprIE fusion protein were generated with retroviral vectors. Expression of the VprCAT or the VprIE fusion protein in CD4+ Jurkat T cells did not interfere with cellular viability or growth but conferred substantial resistance to HIV replication. The resistance to HIV replication was more pronounced in Jurkat-VprIE cells than in Jurkat-VprCAT cells. Moreover, the antiviral effect mediated by VprIE was dependent on an intact p6(gag) domain, indicating that the impairment of HIV-1 replication required the specific incorporation of Vpr fusion protein into virions. Gene expression, assembly, or release was not affected upon expression of these Vpr fusion proteins. Indeed, the VprIE and VprCAT fusion proteins were shown to affect the infectivity of progeny virus, since HIV virions containing the VprCAT or the VprIE fusion proteins were, respectively, 2 to 3 times and 10 to 30 times less infectious than the wild-type virus. Overall, this study demonstrated the successful transfer of resistance to HIV replication in tissue cultures by use of Vpr-based antiviral genes.

Gene Products, vpr↗
PubMed2003

Specific G2 arrest of caprine cells infected with a caprine arthritis encephalitis virus expressing vpr and vpx genes from simian immunodeficiency virus.

Primate lentivirus (HIV and SIV) vpr accessory genes encode 12- to 14-kDa proteins which induce cell cycle arrest at the G2 phase of infected cells, preventing them from going through mitosis. Members of the HIV-2/SIVmac/SIVsmm group also encode a second closely related accessory protein called Vpx. Vpx and HIV Vpr are critical for virus replication in nondividing cells due to their participation in nuclear import of the preintegration complex. Caprine arthritis encephalitis virus (CAEV) and maedi visna virus are the natural lentiviruses of domestic goat and sheep, respectively, and their genomes do not carry vpr and vpx genes. In this study, we generated chimeric CAEV-based genomes carrying vpr and vpx genes from SIVmac239 and tested their ability to induce G2 cell cycle arrest in infected caprine cells. CAEV-pBSCAvpxvpr is the chimeric genome that was shown to be infectious and replication competent. Our data demonstrated that CAEV-pBSCAvpxvpr-infected goat synovial membrane cell monolayer developed more cytopathic effects and a high proportion of cells remained in the G2 phase of cell cycle. This G2 arrest was observed both at the early and at the late stages of infection, while minimal effect was observed with the parental CAEV-pBSCA. These results, described for the first time in mammalian cells other than those of primates, indicate that Vpr-induced G2 cell cycle arrest is not restricted to only primate cells. Thus, conservation of Vpx/Vpr protein functions in caprine cells suggests a possible role for these proteins in the virus life cycle and its ability to adapt to new hosts. The data presented here thus raise a pertinent question about the biological significance of the conservation of Vpr and Vpx functions in caprine cells despite the high phylogenic distance between primates and small ruminants.

Animals↗
PubMed2006

Morphological study on biologically distinct vpx/vpr mutants of HIV-2.

We have previously shown that human immunodeficiency virus type 2 (HIV-2) without functional vpx and vpr genes is severely defective for viral growth in lymphocytic cells, and suggested that the virions produced in the absence of Vpx and Vpr are critically damaged. To examine the nature of replication-defect for the vpx/vpr double mutant, we quantitatively and morphologically studied the virions produced in cells transfected or infected with wild type clone, single (vpx and vpr mutants) or the double mutant. While no significant difference in virion production was found for various virus clones in transfected cells, a major growth retardation in infected cells was readily observed for the vpx and vpx/vpr mutants. In particular, no viral growth was detected for the double mutant. By contrast to the very distinct growth characteristics of the three mutant clones, no appreciable difference in virion morphology was noted. These results indicated that Vpx and Vpr of HIV-2 may cooperatively contribute to virion infectivity without affecting virion morphogenesis.

Cell Line↗
PubMed2000

Identification of critical amino acid residues in human immunodeficiency virus type 1 IN required for efficient proviral DNA formation at steps prior to integration in dividing and nondividing cells.

Human immunodeficiency virus type 1 integrase (HIV-1 IN) is thought to have several putative roles at steps prior to integration, such as reverse transcription and nuclear transport of the preintegration complex (PIC). Here, we investigated new functional aspects of HIV-1 IN in the context of the viral replication cycle through point mutagenesis of Ser, Thr, Tyr, Lys, and Arg residues conserved in IN, some of which are located at possible phosphorylation sites. Our results showed that mutations of these Ser or Thr residues had no effect on reverse transcription and nuclear transport of PIC but had a slight effect on integration. Of note, mutations in the conserved KRK motif (amino acids 186 to 189), proposed previously as a putative nuclear localization signal (NLS) of HIV-1 IN, did not affect the karyophilic property of HIV-1 IN as shown by using a green fluorescent protein fusion protein expression system. Instead, these KRK mutations resulted in an almost complete lack of viral gene expression due to the failure to complete reverse transcription. This defect was complemented by supplying wild-type IN in trans, suggesting a trans-acting function of the KRK motif of IN in reverse transcription. Mutation at the conserved Tyr 143 (Y143G) resulted in partial impairment of completion of reverse transcription in monocyte-derived macrophages (MDM) but not in rhabdomyosarcoma cells. Similar effects were obtained by introducing a stop codon in the vpr gene (DeltaVpr), and additive effects of both mutations (Y143G plus DeltaVpr) were observed. In addition, these mutants did not produce two-long terminal repeat DNA, a surrogate marker for nuclear entry, in MDM. Thus, the possible impairment of Y143G might occur during the nuclear transport of the PIC. Taken together, our results identified new functional aspects of the conserved residues in HIV-1 IN: i) the KRK motif might have a role in efficient reverse transcription in both dividing and nondividing cells but not in the NLS function; ii) Y143 might be an important residue for maintaining efficient proviral DNA formation in nondividing cells.

Amino Acid Sequence↗
PubMed1993

Context-dependent role of human immunodeficiency virus type 1 auxiliary genes in the establishment of chronic virus producers.

Two molecularly cloned viruses, human immunodeficiency virus type 1 (HIV-1)-NL4-3 (NL4-3) and HIV-1-HXB-2 (HXB-2), have been used to study the role of HIV-1 auxiliary genes in the establishment of chronic virus producers. NL4-3 encodes all known HIV-1 proteins, whereas HXB-2 is defective for three auxiliary genes: vpr, vpu, and nef. Studies were done in H9 cells, a T-cell line unusually permissive for the establishment of chronic virus producers. NL4-3 and HXB-2 undergo lytic phases of infection in H9 cultures with HXB-2, but not NL4-3, supporting the efficient establishment of chronic virus producers. Tests of mutant NL4-3 genomes containing various combinations of defective auxiliary genes revealed that both vpr and nef limited the ability of NL4-3 to establish chronic virus producers. Tests of a series of recombinants between NL4-3 and HXB-2 revealed that 5' internal sequences as well as fragments containing defective auxiliary genes affected the establishment of chronic virus producers. Viral envelope sequences and levels of virus production did not correlate with the ability to establish chronic virus producers. These results suggest that complex interactions of viral auxiliary and nonauxiliary gene functions with the host cell determine the ability to establish chronic virus producers.

Cloning, Molecular↗
PubMed2003

Mechanism of HIV-1 viral protein R-induced apoptosis.

The paradigm of HIV-1 infection includes the diminution of CD4(+) T cells, loss of immune function, and eventual progression to AIDS. However, the mechanisms that drive host T cell depletion remain elusive. One HIV protein thought to participate in this destructive cascade is the Vpr gene product. Accordingly, we review the biology of the HIV-1 viral protein R (Vpr) an apoptogenic HIV-1 accessory protein that is packaged into the virus particle. In this review we focus specifically on Vpr's ability to induce host cell apoptosis. Recent evidence suggests that Vpr implements a unique mechanism to drive host cell apoptosis, by directly depolarizing the mitochondria membrane potential. Vpr's attack on the mitochondria results in release of cytochrome c resulting in activation of the caspase 9 pathway culminating in the activation of caspase 3 and the downstream events of apoptosis. Vpr may interact with the adenine nucleotide translocator (ANT) to prompt this cascade. The role of Vpr-induced apoptosis in HIV pathogenesis is considered.

Apoptosis↗
PubMed2006

Interaction between the HIV-1 protein Vpr and the adenine nucleotide translocator.

The HIV-1 protein Vpr circulates in the serum of seropositive individuals and in the cerebrospinal fluid of AIDS patients with neurological disorders. Vpr triggers apoptosis of numerous cell types after extracellular addition, vpr gene transfer or in the context of viral infection. Moreover, in vivo, transgenic mice over-expressing Vpr have enhanced T lymphocytes apoptosis. In previous studies, we suggested that the Vpr apoptotic activities were because of its binding to the adenine nucleotide translocator (ANT), a mitochondrial ATP/ADP antiporter. To specify this interaction, fragments of both proteins were synthesized and used in biochemical and biophysical experiments. We demonstrate here that in vitro, the (27-51) and (71-82) Vpr peptides bind to a region encompassing the first ANT intermembrane space loop and part of its second and third transmembrane helices. Computational analysis using a docking program associated to dynamic simulations enabled us to construct a three-dimensional model of the Vpr-ANT complex. In this model, the N-terminus of Vpr plunges in the ANT cavity whereas the Vpr C-terminal extremity is located at the surface of the ANT allowing possible interactions with a third partner. These results could be used to design molecules acting as pro-apoptotic Vpr analogs or as apoptosis inhibitors preventing the Vpr-ANT interaction.

Animals↗
PubMed1998

The HIV-1 Vpr displays strong anti-apoptotic activity.

Mutations in the human immunodeficiency virus type 1 (HIV-1) vpr gene only slightly reduce the replication rate of the virus. To study the role of HIV-1 Vpr in biological effects on cells, HEp-2 cells, which express HIV-1 Vpr constitutively but at a low level, were established. While control HEp-2 cells underwent apoptosis when incubated with sorbitol, the morphological and biochemical apoptotic changes were inefficiently induced in the HIV-1 Vpr-expressing cells by the same treatment. These results clearly indicate that HIV-1 Vpr has anti-apoptotic activity, and raise the possibility that Vpr acts as a weak activator of virus replication through anti-apoptosis.

Animals↗
PubMed2001

A defect in HIV-1 transgenic murine macrophages results in deficient nitric oxide production.

HIV transgenic mice bearing multiple copies of a noninfectious (Deltagag/pol) proviral DNA were tested for the systemic production of nitric oxide (NO). Serum levels of NO metabolites were reduced about 50% in HIV transgenic mice compared with nontransgenic sibling mice. This difference persisted when NO production was induced with peritoneal injections of bacterial endotoxin (LPS). Peritoneal inflammatory macrophages, but not resident peritoneal macrophages, derived from HIV-1 transgenic mice and activated in vitro with LPS and IFN-gamma (or tumor necrosis factor alpha and IFN-gamma) also produced about 50% less NO than did macrophages harvested from nontransgenic littermates. Isogenic, transgenic mice bearing mutated nef or vpr genes had normal serum levels of NO metabolites and their macrophages produced normal levels of NO when stimulated. An explanation for the reduced NO response of HIV[Vpr+Nef+] macrophages was not apparent from measured levels of iNOS expression, viral gene expression, or arginase activity in activated macrophages. Inhibition of nitric oxide synthase (NOS) isoforms with L-NAME or aminoguanidine blocked time-dependent increases in HIV gene expression in activated macrophages cultured ex vivo. Inhibition with L-NAME occurred despite high levels of NO generated by iNOS, and exogenously supplied NO induced HIV gene expression only weakly, suggesting that cNOS had the greater influence on proviral gene induction. This system is presented as a model of HIV-1 proviral gene expression and dysfunction in macrophages.

Animals↗
PubMed2001

HIV-1 Vpr enhances viral burden by facilitating infection of tissue macrophages but not nondividing CD4+ T cells.

Prior experiments in explants of human lymphoid tissue have demonstrated that human immunodeficiency virus type 1 (HIV-1) productively infects diverse cellular targets including T cells and tissue macrophages. We sought to determine the specific contribution of macrophages and T cells to the overall viral burden within lymphoid tissue. To block infection of macrophages selectively while preserving infection of T cells, we used viruses deficient for viral protein R (Vpr) that exhibit profound replication defects in nondividing cells in vitro. We inoculated tonsil histocultures with matched pairs of congenic viruses that differed only by the presence of a wild-type or truncated vpr gene. Although these viruses exhibited no reduction in the infection or depletion of T cells, the ability of the Vpr-deficient R5 virus to infect tissue macrophages was severely impaired compared with matched wild-type R5 virus. Interestingly, the Vpr-deficient R5 virus also exhibited a 50% reduction in overall virus replication compared with its wild-type counterpart despite the fact that macrophages represent a small fraction of the potential targets of HIV-1 infection in these tissues. Collectively, these data highlight the importance of tissue macrophages in local viral burden and further implicate roles for CC chemokine receptor 5, macrophages, and Vpr in the life cycle and pathogenesis of HIV-1.

CD4-Positive T-Lymphocytes↗
PubMed1994

Serum Vpr regulates productive infection and latency of human immunodeficiency virus type 1.

In human immunodeficiency virus (HIV)-positive individuals, the vast majority of infected peripheral blood cells and lymph node cells may be latently or nonproductively infected. The vpr open reading frame of HIV-1 encodes a 15-kDa virion-associated protein, Vpr. The vpr gene has been shown to increase virus replication in T cells and monocyte/macrophages in vitro. We have previously reported that vpr expression in various tumor lines leads to growth inhibition and differentiation, indicating that Vpr may function as a regulator of cellular permissiveness to HIV replication. Here we show that Vpr protein is present in significant amounts in the serum of AIDS patients. Purified serum Vpr activated virus expression from five latently infected cell lines, U1, OM.10.1, ACH-2, J1.1, and LL58. Serum Vpr also activated virus expression from resting peripheral blood mononuclear cells of HIV-infected individuals. Together, these findings implicate serum Vpr in the activation of HIV replication in vivo and in the control of latency. Anti-Vpr antibodies inhibited Vpr activity, suggesting that humoral immunity modulates Vpr activity in vivo. These results have broad implications for the virus life cycle and for the prospective control of HIV replication and pathogenesis.

Acquired Immunodeficiency Syndrome↗
PubMed2002

HIV-1 Vpr induces apoptosis through caspase 9 in T cells and peripheral blood mononuclear cells.

Human immunodeficiency virus, type 1 (HIV-1), vpr gene encodes a 14-kDa virion-associated protein, which exhibits significant effects on human cells. One important property of Vpr is its ability to induce apoptosis during infection. Apoptotic induction is likely to play a role in the pathogenesis of AIDS. However, the pathway of apoptosis is not clearly defined. In this report we investigate the mechanism of apoptosis induced by HIV-1 Vpr using a Vpr pseudotype viral infection system or adeno delivery of Vpr in primary human lymphoid cells and T-cells. With either vector, HIV-1 Vpr induced cell cycle arrest at the G(2)/M phase and apoptosis in lymphoid target cells. Furthermore, we observed that with both vectors, caspase 9, but not caspase 8, was activated following infection of human peripheral blood mononuclear cell with either Vpr-positive HIV virions or adeno-delivered Vpr. Activation of the caspase 9 pathway resulted in caspase 3 activation and apoptosis in human primary cells. These effects were coincident with the disruption of the mitochondrial transmembrane potential and induction of cytochrome c release by Vpr. The Vpr-induced signaling pathway did not induce CD95 or CD95L expression. Bcl-2 overexpressing cells succumb to Vpr-induced apoptosis. These studies illustrate that Vpr induces a mitochondria-dependent apoptotic pathway that is distinct from apoptosis driven by the Fas-FasL pathway.

Annexin A5↗
PubMed1998

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) interacts with Lys-tRNA synthetase: implications for priming of HIV-1 reverse transcription.

The vpr gene of human immunodeficiency virus type 1 (HIV-1) encodes a 96-amino-acid 14-kDa protein (viral protein R [Vpr]), which is produced late in the viral life cycle and is incorporated into the virion. Although Vpr is not required for viral replication in transformed cell lines and primary T lymphocytes, it is essential for productive infection of macrophages and monocytes and appears to be important for pathogenesis in vivo. To establish the role of Vpr in HIV-1 replication and pathogenesis, we have isolated cellular proteins with which Vpr interacts. By using the yeast two-hybrid system, Lys-tRNA synthetase (LysRS) was identified as a Vpr-interacting protein. The interaction between Vpr and LysRS was characterized both in vitro and in vivo, and the domains of Vpr required for the interaction were defined. In the presence of Vpr, LysRS-mediated amino-acylation of tRNA(Lys) is inhibited. Since tRNA(Lys) is the primer for reverse transcription of the HIV-1 genome, this suggests that the interaction between Vpr and LysRS may influence the initiation of HIV-1 reverse transcription.

Acylation↗
PubMed1996

Genetic control of infection of primary macrophages with T-cell-tropic strains of HIV-1.

Human immunodeficiency virus type 1 (HIV-1) NDK, a Zairian subtype D virus highly cytopathic for CD4-positive lymphocytes, and the prototype subtype B virus HIV-1 LAV are about 10(4) and 10(5) times more infectious, respectively, for T lymphocytes than for blood-derived macrophages (BDM). Recombinant viruses derived from HIV-1 LAV and HIV-1 NDK were used to determine the genetic control and the step of the virus/cell cycle responsible for infection of BDM with T-cell-tropic viruses. We found that recombinants bearing the envelope glycoprotein of HIV-1 NDK are able to enter more efficiently into BDM than recombinants with HIV-1 LAV envelope glycoprotein. We also found that a genetic region outside of the env gene is responsible for production of HIV-1 NDK infectious progeny from BDM. This region consists of the vif gene and the C- and N-terminal portions of pol and vpr genes, respectively. Our results suggest that productive infection of primary macrophages with T-cell-tropic strains of HIV-1 is determined by two different genetic mechanisms: one effective at the virus/cell entry, controlled by the env gene, and the second after entry, controlled by genes vif and vpr. In comparison with HIV-1 LAV, HIV-1 NDK has been able to more easily overcome both restriction mechanisms.

Cell Line↗
PubMed2001

Changing epidemiology of HIV type 1 infections in India: evidence of subtype B introduction in Bombay from a common source.

India has experienced multiple introductions of diverse HIV-1 subtypes A, B, C, and E, along with subtype B of HIV-2 between the 1980s and early 1990s. In this study, we have carried out a molecular investigation of 21 heterosexually and vertically acquired HIV-infected individuals from the New Bombay area, who tested positive for HIV-1 by commercial enzyme-linked immunosorbent assay (ELISA) and Western blot assay. We have sequenced the proviral DNA segments from the uncultured PBMCs in the hypervariable env V(3) region (286 bp) and a full-length vpr gene (291 bp). Overall, phylogenetic clustering of all Indian strains and also their clustering with subtype B strains were evident from both V(3)- and vpr gene-based trees, strongly supporting their recent introduction from a common source. This is the first report on subtype B introduction in Bombay, a region where subtype C predominates. Overall, these subtype B strains from Bombay shared genetic closeness with subtype B strains from Europe, the United States, and Asia.

Adult↗
PubMed1997

Nuclear import, virion incorporation, and cell cycle arrest/differentiation are mediated by distinct functional domains of human immunodeficiency virus type 1 Vpr.

The vpr gene product of human immunodeficiency virus type 1 (HIV-1) is a virion-associated protein that is essential for efficient viral replication in monocytes/macrophages. Vpr is primarily localized in the nucleus when expressed in the absence of other viral proteins. Vpr is packaged efficiently into viral particles through interactions with the p6 domain of the Gag precursor polyprotein p55gag. We developed a panel of expression vectors encoding Vpr molecules mutated in the amino-terminal helical domain, leucine-isoleucine (LR) domain, and carboxy-terminal domain to map the different functional domains and to define the interrelationships between virion incorporation, nuclear localization, cell cycle arrest, and differentiation functions of Vpr. We observed that substitution mutations in the N-terminal domain of Vpr impaired both nuclear localization and virion packaging, suggesting that the helical structure may play a vital role in modulating both of these biological properties. The LR domain was found to be involved in the nuclear localization of Vpr. In contrast, cell cycle arrest appears to be largely controlled by the C-terminal domain of Vpr. The LR and C-terminal domains do not appear to be essential for virion incorporation of Vpr. Interestingly, we found that two Vpr mutants harboring single amino acid substitutions (A30L and G75A) retained the ability to translocate to the nucleus but were impaired in the cell cycle arrest function. In contrast, mutation of Leu68 to Ser resulted in a protein that localizes in the cytoplasm while retaining the ability to arrest host cell proliferation. We speculate that the nuclear localization and cell cycle arrest functions of Vpr are not interrelated and that these functions are mediated by separable putative functional domains of Vpr.

Amino Acid Sequence↗