The host restriction factor TRIM5␣ mediates species-specific, early blocks to retrovirus infection; susceptibility to these blocks is determined by viral capsid sequences. Here we demonstrate that TRIM5␣ variants from Old World monkeys specifically associate with the HIV type 1 (HIV-1) capsid and that this interaction depends on the TRIM5␣ B30.2 domain. Human and New World monkey TRIM5␣ proteins associated less efficiently with the HIV-1 capsid, accounting for the lack of restriction in cells of these species. After infection, the expression of a restricting TRIM5␣ in the target cells correlated with a decrease in the amount of particulate capsid in the cytosol. In some cases, this loss of particulate capsid was accompanied by a detectable increase in soluble capsid protein.Inhibiting the proteasome did not abrogate restriction. Thus, TRIM5␣ restricts retroviral infection by specifically recognizing the capsid and promoting its rapid, premature disassembly.

Background The efficacy of various antiretroviral (ARV) therapy regimens for human immunodeficiency virus type 2 (HIV-2) infection remains unclear. HIV-2 is intrinsically resistant to the nonnucleoside reverse-transcriptase inhibitors and to enfuvirtide and may also be less susceptible than HIV-1 to some protease inhibitors (PIs). However, the mutations in HIV-2 that confer ARV resistance are not well characterized. Methods Twenty-three patients were studied as part of an ongoing prospective longitudinal cohort study of ARV therapy for HIV-2 infection in Senegal. Patients were treated with nucleoside reverse-transcriptase inhibitor (NRTI)– and PI (indinavir)–based regimens. HIV-2 pol genes from these patients were genotyped, and the mutations predictive of resistance in HIV-2 were assessed. Correlates of ARV resistance were analyzed. Results Multiclass drug–resistance mutations (NRTI and PI) were detected in strains in 30% of patients; 52% had evidence of resistance to at least 1 ARV class. The reverse-transcriptase mutations M184V and K65R, which confer high-level resistance to lamivudine and emtricitabine in HIV-2, were found in strains from 43% and 9% of patients, respectively. The Q151M mutation, which confers multinucleoside resistance in HIV-2, emerged in strains from 9% of patients. HIV-1–associated thymidine analogue mutations (M41L, D67N, K70R, L210W, and T215Y/F) were not observed, with the exception of K70R, which was present together with K65R and Q151M in a strain from 1 patient. Eight patients had HIV-2 with PI mutations associated with indinavir resistance, including K7R, I54M, V62A, I82F, L90M, L99F; 4 patients had strains with multiple PI resistance–associated mutations. The duration of ARV therapy was positively associated with the development of drug resistance (P = .02). Nine (82%) of 11 patients with HIV-2 with detectable ARV resistance had undetectable plasma HIV-2 RNA loads (<1.4 log10 copies/mL), compared with 3 (25%) of 12 patients with HIV-2 with detectable ARV resistance (P = .009). Patients with ARV-resistant virus had higher plasma HIV-2 RNA loads, compared with those with non–ARV-resistant virus (median, 1.7 log10 copies/mL [range, <1.4 to 2.6 log10 copies/mL] vs. <1.4 log10 copies/mL [range, <1.4 to 1.6 log10 copies/mL]; P = .003). Conclusions HIV-2–infected individuals treated with ARV therapy in Senegal commonly have HIV-2 mutations consistent with multiclass drug resistance. Additional clinical studies are required to improve the efficacy of primary and salvage treatment regimens for treating HIV-2 infection.

Genotypic surveys suggest that human immunodeficiency virus type 1 (HIV-1) and HIV-2 evolve different sets of mutations in response to nucleoside reverse-transcriptase inhibitors (NRTIs). We used site-directed mutagenesis, culture-based phenotyping, and cell-free assays to determine the resistance profiles conferred by specific amino acid replacements in HIV-2 reverse transcriptase. Although thymidine analogue mutations had no effect on zidovudine sensitivity, the addition of Q151M together with K65R or M184V was sufficient for high-level resistance to both lamivudine and zidovudine in HIV-2, and the combination of K65R, Q151M, and M184V conferred classwide NRTI resistance. These data suggest that current NRTI-based regimens are suboptimal for treating HIV-2 infection.

Using an indicator cell assay that directly quantifies viral replication, we show that human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2, respectively) exhibit similar sensitivities to 3-azido-3-deoxythymidine (zidovudine) as well as other nucleoside analog inhibitors of reverse transcriptase. These data support the use of nucleoside analogs for antiviral therapy of HIV-2 infection.

Human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) contains four structural motifs (A, B, C, and D) that are conserved in polymerases from diverse organisms. Motif B interacts with the incoming nucleotide, the template strand, and key active-site residues from other motifs, suggesting that motif B is an important determinant of substrate specificity. To examine the functional role of this region, we performed "random scanning mutagenesis" of 11 motif B residues and screened replication-competent mutants for altered substrate analog sensitivity in culture. Single amino acid replacements throughout the targeted region conferred resistance to lamivudine and/or hypersusceptibility to zidovudine (AZT). Substitutions at residue Q151 increased the sensitivity of HIV-1 to multiple nucleoside analogs, and a subset of these Q151 variants was also hypersusceptible to the pyrophosphate analog phosphonoformic acid (PFA). Other AZT-hypersusceptible mutants were resistant to PFA and are therefore phenotypically similar to PFA-resistant variants selected in vitro and in infected patients. Collectively, these data show that specific amino acid replacements in motif B confer broad-spectrum hypersusceptibility to substrate analog inhibitors. Our results suggest that motif B influences RT-deoxynucleoside triphosphate interactions at multiple steps in the catalytic cycle of polymerization.Conversion of viral RNA to double-stranded DNA by reverse transcriptase (RT) is a defining step in the retroviral life cycle (8) and a key target of therapy for human immunodeficiency virus type 1 (HIV-1) infection (17). The 66-kilodalton subunit of HIV-1 RT contains four motifs (A, B, C, and D) that are similarly arranged in all known structures of replicative DNA and RNA polymerases (21). Three additional structural elements, motifs E and F and premotif A, are also conserved among RTs and viral RNA-dependent RNA polymerases (4,21,45,76). Together, motifs A, B, C, and F and premotif A form a closely packed protein framework that positions the templating nucleotide, the primer terminus, and incoming deoxynucleoside triphosphate (dNTP) at the RT active site (Fig. 1A). Amino acid substitutions within this conserved core can affect dNTP insertion fidelity, susceptibility to nucleoside analogs, and/or discrimination against ribonucleoside triphosphates (rNTPs) during DNA synthesis (40,49,64,72). Thus, these motifs influence the stringency and specificity of substrate incorporation by RT.Motif B is of particular interest because of its central position in the RT core structure (Fig. 1) (12, 24). Motif B contacts the template strand, the incoming dNTP, and each of the other motifs in the core structure (premotif A and motifs A, C, and F) (Fig. 1A), including residues within these other motifs that are known to affect dNTP substrate recognition (Fig. 1B) (12, 24). The importance of motif B in substrate selection is evident from studies of HIV-1 mutants resistant to nucleoside analogs (49, 72). Two amino acid substitutions in motif B a...