HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 VIF DOES NOT INFLUENCE EXPRESSIONOR VIRION INCORPORATION OF GAG-ENCODED, POL-ENCODED, AND ENV-ENCODED PROTEINS

The Vif protein of human immunodeficiency virus type 1 is required for productive replication in peripheral blood lymphocytes and a limited number of immortalized T-lymphoid lines (nonpermissive cells), In cont rast, Vif is fully dispensable for virus replication in other T-cell l ines (permissive cells), Because the infection phenotype of released v irions is determined by producer cells and by the presence of Vif in t hose cells, we have analyzed the protein contents of purified viral pa rticles in an attempt to define compositional differences that could e xplain the infection phenotype. Surprisingly, we were unable to discer n any Vif- or cell-type-dependent quantitative or qualitative differen ce in the Gag, pol, and Env proteins of virions or virus-producing cel ls that correlates with virus infectivity. We were, however, able to d emonstrate that Vif itself is present in virions and, using semiquanti tative Western blotting (immunoblotting), that there is an average of 30 to 80 molecules of Vif incorporated into each virion. Importantly, parallel analyses of total lysates of the producer cells revealed that the cell-associated expression levels of Vif are close to those of th e Gag proteins, Given the dramatically higher abundance of Vif in cell s than in virions, we speculate that Vif exerts its principal activity during the processes of virus assembly and budding and that this func tion could be of a structural-conformational nature.