Role of the gag matrix domain in targeting human immunodeficiency virus type 1 assembly

Human immunodeficiency virus type 1 (HIV-1) particle formation and the subs equent initiation of protease-mediated maturation occur predominantly on th e plasma membrane. However, the mechanism by which HIV-1 assembly is target ed specifically to the plasma membrane versus intracellular membranes is la rgely unknown. Previously, we observed that mutations between residues 84 a nd 88 of the matrix (MA) domain of HIV-1 Gag cause a retargeting of virus p article formation to an intracellular site. In this study, we demonstrate t hat the mutant virus assembly occurs in the Golgi or in post-Golgi vesicles . These particles undergo core condensation in a protease-dependent manner, indicating that virus maturation can occur not only on the plasma membrane but also in the Golgi or post-Golgi vesicles. The intracellular assembly o f mutant particles is dependent on Gag myristylation but is not influenced by p6(Gag) or envelope glycoprotein expression, Previous characterization o f viral revertants suggested a functional relationship between the highly b asic domain of MA (amino acids 17 to 31) and residues 84 to 88, We now demo nstrate that mutations in the highly basic domain also retarget virus parti cle formation to the Golgi or post-Golgi vesicles. Although the basic domai n has been implicated in Gag membrane binding, no correlation was observed between the impact of mutations on membrane binding and Gag targeting, indi cating that these two functions of MA are genetically separable. Plasma mem brane targeting of Gag proteins with mutations in either the basic domain o r between residues 84 and 88 was rescued by coexpression with wild-type Gag ; however, the two groups of MA mutants could not rescue each other. We pro pose that the highly basic domain of MA contains a major determinant of HIV -1 Gag plasma membrane targeting and that mutations between residues 84 and 88 disrupt plasma membrane targeting through an effect on the basic domain .