Assembly and processing of human immunodeficiency virus gag mutants containing a partial replacement of the matrix domain by the viral protease domain

We constructed human immunodeficiency virus (HIV) mutants by replacing the matrix domain with sequences encoding the viral protease or p6* and proteas e; The chimeras retaining matrix myristylation and processing signals under went efficient autoprocessing with severely defective particle budding. The budding defects of the chimeras were rescued by suppressing the chimera pr otease activity either through addition of an HN protease inhibitor or thro ugh inactivating the chimera protease via a substitution mutation of the ca talytic aspartic acid residue. This resulted in the release of chimeric vir us-like particles with the density of a wild-type retrovirus particle. In a ddition, the assembly-competent but processing:defective chimeras produced proteolytically processed particles with significant reverse transcriptase activity when a downstream native pol gene was present. These results sugge st that HIV has the potential to adapt heterologous sequences in place of t he matrix sequence without major effects on virus-like particle budding. In addition, the positions of the protease and substrate accessibility may co ntribute significantly toward avoiding a premature Gag or Gag-Pol process, which leads to severe defects in both particle budding and incorporation.