The human immunodeficiency virus type 1 Vif protein modulates the postpenetration stability of viral nucleoprotein complexes

Abstract

The vif gene of human immunodeficiency virus type 1 is absolutely required for productive infection of primary cells derived from human blood and certain immortalized T lymphoid cells, for example, H9. Cells with this restrictive phenotype are termed nonpermissive, whereas cell lines in which vif-deficient virus can replicate efficiently are known as permissive. In this paper, we describe experiments in which virus stocks derived from single-cycle infections of strictly nonpermissive H9 cells were used to determine the fate of vif-deficient infections. By PCR-based approaches, it was found that Vif has no significant impact on the biosynthetic capability of the virion reverse transcriptase in infected C8166 T cells. Specifically, the initial appearance of all DNA species up to and including initiated second (plus) strands as well as the early accumulation of these replicative intermediates is equivalent for wild-type and vif-deficient infections. However, whereas these viral DNAs are stably maintained in wild-type infections and can proceed to establish proviruses, they are largely degraded by the later time points of vif-deficient infections and, as a result, are prevented from forming proviruses. Subcellular fractionation analyses indicated that the majority of viral DNA is localized to the nucleus within 2 h of infection and that the turnover of reverse transcripts that occurs in these vif-deficient infections presumably takes place in the nucleus. Given that the ultimate infection phenotype of the virions is determined during virus production, we propose that Vif is required for an aspect of virus assembly and/or maturation that endows penetrating viral nucleoprotein cores with the ability to mature into functional preintegration complexes that can proceed to provirus establishment. In contrast, viruses that are produced in the absence of Vif give rise to nucleoprotein complexes that disassemble prematurely in challenged cells and fail to protect their RNA/DNA contents from nucleolytic destruction.