Simon JHM, Fouchier RAM, Malim MH Howard Hughes Medical Institute and Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA.
Productive infection of primary cells by HIV-1 requires a functional Vif protein. Previous analyses have demonstrated that Vif must be present during the processes of virion assembly and/or maturation. Using PCR-based assays. we have shown that vif-defective HIV-1 appears to penetrate cells slightly less efficiently than wild type virus. However, once entry has taken place, reverse transcription, at least to the point of the second strand transfer, proceeds in a manner that is indistinguishable from a wild type infection. At later times, the levels of newly synthesized viral DNA diminish markedly in the absence of Vif and provirus formation fails to occur to a significant degree, probably as a result of virion and/or capsid instability. In addition, we have performed two-dimensional gel electrophoretic analyses of metabolically labeled, sucrose gradient purified virions. In our initial analyses, it is clear that the levels of p24 Gag (CA) are dramatically reduced in the absence of Vif. This suggests that the Vif protein is required for the complete proteolytic processing of the p55 Gag polyprotein and that a failure to undergo the necessary cleavages inhibits virus infectivity.
