Partial rescue of the Vif-negative phenotype of mutant human immunodeficiency virus type 1 strains from nonpermissive cells by intravirion reverse transcription

Virion infectivity factor (Vif) is a protein encoded by human immunodeficie ncy virus type I (HIV-1) and is essential for viral replication. It appears that Vif functions in the virus-producing cells and affects viral assembly . Viruses with defects in the vif gene (vif-) generated from the "nonpermis sive cells" are not able to complete reverse transcription. In previous stu dies, it was demonstrated that defects in the vif gene also affect endogeno us reverse transcription (ERT) when mild detergents were utilized to permea bilize the viral envelope. In this report, we demonstrate that defects in t he vif gene have much less of an effect on ERT if detergent is not used. Wh en ERT was driven by addition of deoxyribonucleoside triphosphates (dNTPs) at high concentrations, certain levels of plus-strand viral DNA could also be achieved. Interestingly, if vif- viruses, generated from nonpermissive c ells and harboring large quantities of viral DNA generated by ERT, were all owed to infect permissive cells, they could partially bypass the block at i ntracellular reverse transcription, through which vif- viruses without dNTP treatment could not pass. Consequently, viral infectivity can be partially rescued from the vif- phenotype. Based on our observations, we suggest tha t vif defects may cause the reverse transcription complex (RT complex) to b ecome sensitive to mild detergent treatments within HIV-1 virions and becom e unstable in the target tells, such that the process of reverse transcript ion cannot be efficiently supported. Further dissection of RT complexes of vif- viruses may be key to uncovering the molecular mechanism(s) of Vif in HIV-1 pathogenesis.