In an assembly-competent Gag/PR context, the wt LZ insertion resulted in markedly reduced, PR activity-dependent virus production (Fig. 2) . Cellular Pr55 gag was barely detected in PRWWz at 12 and 24 h post-transfection, while most Pr55 gag remained unprocessed in wt transfectants 12 h post-transfection (data not shown). Combined, these results suggest that LZenhanced Gag cleavage is associated with premature Gag processing due to premature PR activation. We suggest that when fused at the PR C-terminus, the LZ domain facilitates PR-PR interaction via enhanced interactions among MA-CA-NC-PR-LZ chimeras. Gag is subsequently cleaved by PR in trans, either by PR embedded in the chimera, or by a mature and fully processed PR dimer.