Role of Vif in Stability of the Human Immunodeficiency Virus Type 1 Core

Abstract

The Vif protein of human immunodeficiency virus type 1 (HIV-1) is important for virion infectivity. Previous studies have shown that vif-defective virions exhibit structural abnormalities in the virus core and are defective in the ability to complete proviral DNA synthesis in acutely infected cells. We developed novel assays to assess the relative stability of the core in HIV-1 virions. Using these assays, we examined the role of Vif in the stability of the HIV-1 core. The integrity of the core was examined following virion permeabilization or removal of the lipid envelope and treatment with various triggers, including S100 cytosol, deoxynucleoside triphosphates, detergents, NaCl, and buffers of different pH to mimic aspects of the uncoating and disassembly process which occurs after virus entry but preceding or during reverse transcription. vif mutant cores were more sensitive to disruption by all triggers tested than wild-type cores, as determined by endogenous reverse transcriptase (RT) assays, biochemical analyses, and electron microscopy. RT and the p7 nucleocapsid protein were released more readily from vif mutant virions than from wild-type virions, suggesting that the internal nucleocapsid is less stably packaged in the absence of Vif. Purified cores could be isolated from wild-type but not vif mutant virions by sedimentation through detergent-treated gradients. These results demonstrate that Vif increases the stability of virion cores. This may permit efficient viral DNA synthesis by preventing premature degradation or disassembly of viral nucleoprotein complexes during early events after virus entry.

Comprehensive Investigation of the Molecular Defect in vif -Deficient Human Immunodeficiency Virus Type 1 Virions

“…Studies have suggested that either reverse transcription fails to proceed to completion or that reverse transcripts are unstable, possibly depending on the identity of the target cell (14,15,18,46,60,67). Correspondingly, several groups have found ⌬vif virions to be par-tially defective in endogenous reverse transcriptase (RT) assays (17,18,27,46,48). Whether these findings are indicative of a specific problem with the reverse transcription complex, structural abnormalities in the viral core (6,9,32,48), or some other molecular defect in virions is unknown.…”

“…Correspondingly, several groups have found ⌬vif virions to be par-tially defective in endogenous reverse transcriptase (RT) assays (17,18,27,46,48). Whether these findings are indicative of a specific problem with the reverse transcription complex, structural abnormalities in the viral core (6,9,32,48), or some other molecular defect in virions is unknown. To date, no reproducible quantitative or qualitative difference in the protein content of wild-type and ⌬vif virions has been reported, aside from a difference in Vif incorporation (6,11,22,38,39,42,61) and a controversial difference in Gag processing (6,56).…”

Vif Overcomes the Innate Antiviral Activity of APOBEC3G by Promoting Its Degradation in the Ubiquitin-Proteasome Pathway

“…Infection was measured 48 h after infection by performing luciferase assays (Promega). Infections of H9 or SupT1 cells were initiated by co-culture with virus-producing 293T cells (23). After overnight incubation, H9 or SupT1 cells were removed, washed, and cultured in RPMI medium with 10% fetal bovine serum.…”

“…Viruses were quantitated by reverse transcriptase assays, and similar amounts were used to infect the reporter cell line Cf2-luc (23). Infection was measured 48 h after infection by performing luciferase assays (Promega).…”

Roles of HIV-1 auxiliary proteins in viral pathogenesis and host-pathogen interactions

“…Proteaseprocessed Vif is believed to be an important step for production of infectious viruses [87]. Vif also stabilizes viral nucleoprotein complex through direct interaction with 5' region of HIV-1 genomic RNA [88][89][90][91]. Moreover, Vif modulates viral reverse transcriptase through its C-terminal domain either by stimulating the binding of RT and primer or increasing the polymerization rate of RT [92].…”