The N-terminal matrix domain of HIV-1 gag is sufficient but not necessary for viral protein U-mediated enhancement of particle release through a membrane-targeting mechanism

Viral protein U (Vpu) is an 81 amino acid phosphoprotein found in human imm unodeficiency virus type 1 (HIV-l)-infected cells. One function of Vpu is t o enhance the release of virus particles from the plasma membrane in infect ed cells. Using subcellular fractionation, we observed that Vpu promotes th e targeting of Pr55 Gag to the plasma membrane, the site of viral assembly. Deletions of Pr55, which removed most of the N-terminal matrix domain (p39 ) or the C-terminal domains of nucleocapsid and p6 (p41), still allowed for virus-like particle production. Moreover, the release of these particles r emained Vpu-responsive. The N-terminal matrix (MA) domain of Gag, which con tains its membrane-binding domain, is sufficient for Vpu-mediated enhanced release into the supernatant. Furthermore, a MA-GFP fusion protein showed e nhanced membrane binding in the presence of Vpu. This demonstrates that Vpu action may be mediated by allowing Gag, specifically the N-terminal matrix domain, to efficiently associate with the plasma membrane. Thus MA appears sufficient but not necessary for Vpu-mediated enhanced particle release, ( C) 2000 Academic Press.