The dominant-negative action of a fusion protein containing the cytoplasmic domain of human immunodeficiency virus type 1 transmembrane protein gp41 in virus replication.

We previously described a novel mode of downregulation of human immunodeficiency virus type 1 (HIV-1) Gag expression by a cytoplasmic domain fusion protein of the envelope (Env) transmembrane protein, beta-galactosidase (beta-gal)/706-856, which contains the cytoplasmic tail of gp41 fused at the C terminus of Escherichia coli beta-gal. In the present study, we showed that this mediator conferred a dose-dependent dominant interference with virus infectivity. In the context of an HIV-1 provirus, this inhibitor downregulated steady-state Env expression. Paradoxically, Env overexpression suppressed beta-gal/706-856-mediatd Gag downregulation. Sucrose gradient ultracentrifugation and confocal microscopy revealed that Gag, Env, and beta-gal/706-856 had stable interactions and formed aggregated complexes in perinuclear regions. Moreover, Env overexpression hindered colocalization of Gag with beta-gal/706-856 in the perinuclear region. Further cytoplasmic domain mapping analyses showed a correlation between the ability of cytoplasmic subdomains to downregulate Gag expression and the ability of these subdomains to stably interact with Gag. These studies show that redirection of Gag from its cytoplasmic synthesis site to a perinuclear compartment is a prerequisite for beta-gal/706-856-mediated Gag downregulation. The results also illustrate that the dynamic interplay among Gag, Env, and beta-gal/706-856 can modulate Gag and Env expression, thus controlling HIV-1 infection.