Biochemical analyses of the interactions between human immunodeficiency virus type 1 Vpr and p6(Gag)

The nonstructural human immunodeficiency virus type 1 Vpr protein is packag ed into progeny virions at significant levels (similar to 200 copies/virion ). Genetic analyses have demonstrated that efficient Vpr packaging is depen dent upon a leucine-X-X-leticine-phenylalanine (LXXLF) motif located in the p6(Gag) domain of the structural Gag polyprotein. Recombinant proteins spa nning full-length Vpr (Vpr(1-97)) or the amino-terminal 71 amino acids (Vpr (1-71)) formed specific complexes with recombinant p6 proteins in vitro. Co mplex formation required an intact LXXLF motif and exhibited an intrinsic d issociation constant of similar to 75 muM. Gel filtration and cross-linking analyses further revealed that Vpr(1-71) self-associated in solution. Our experiments demonstrate that Vpr can bind directly and specifically to p6 a nd suggest that oligomerization of both Vpr and Gag may serve to increase t he avidity and longevity of Vpr-Gag complexes, thereby ensuring efficient V pr packaging.