To determine whether the PRWz or PRWWz assembly defect is directly associated with viral PR activity, we treated PRWz and PRWWz transfectants with Saquinavier, an HIV-1 PR inhibitor (designated as PI). As expected, virus-associated PRWWz Gag (Pr55 gag and p41 gag ) that was previously undetectable (or barely detectable) became readily detectable when PI concentrations were gradually increased (Fig. 3A) . We noticed that wt cellular p24 gag was still easily detected, even though PRWWz p24 gag was undetectable under the same treatment conditions (Fig. 3A , lanes 3 vs. 7). This suggests that PRWWz is more susceptible to a protease inhibitor than wt, despite having higher Gag cleavage efficiency.