Overexpression and Incorporation of GagPol Precursor Does Not Impede Packaging of HIV-1 tRNALys3 but Promotes Intracellular Budding of Virus-Like Particles

Abstract

We have recently demonstrated that alteration of the human immunodeficiency virus type 1 (HIV-1) Gag/GagPol ratio in virus-producing cells reduces the infectivity of progeny viruses and hinders the formation of stable virion RNA dimers without impairing virion packaging of the viral genomic RNA. In addition, we have previously shown that the expression of GagPol mediates the selective packaging of tRNA^Lys3. In this study we report that overexpression of uncleaved GagPol in the virus-producing cell did not alter the packaging levels of tRNA^Lys3. Similarly, altering the virion-associated Gag/GagPol ratio did not affect the virion packaging of the HIV-1 envelope protein nor cyclophilin A. Thin section electron microscopy analysis of the cells overexpressing protease-defective [PR(–)] GagPol revealed immature virions but no mature virions. These immature virions were seen both extracellularly and in membrane-bound cytoplasmic vacuoles. Furthermore, an accumulation of electron-dense material was occasionally found at the plasma membrane and associated with intracytoplasmic membranous vacuoles in cells expressing excess PR(–) GagPol. No intracellular HIV was seen in the wild-type control. Density gradient analysis showed that the overall density of these mutant virions with excess PR(–) GagPol was identical to that of the wild-type HIV-1. The findings indicate that overexpression of PR(–) GagPol, in the presence of Gag synthesis, promotes intracellular budding of the mutant virions and inhibits virus maturation.