Protein stability influences human immunodeficiency virus type 2 Vpr virion incorporation and cell cycle effect

Using recombinant proteins as standards, we calculated the amount of Vpr and Vpx present in HIV-2ROD particles. We find 2000-3000 copies of Vpx per particle but only 40-50 copies of Vpr. We investigated the reasons for this discrepancy between Vpx and Vpr and found that viral factors, including HIV-2 Vpx, do not restrict its incorporation. Instead, the accumulation of HIV-2ROD Vpr during infection is restricted by a short protein half-life which acts to limit its virion incorporation. The half-life of HIV-2 Vpr was calculated to be about 90 min, while HIV-2 Vpx and HIV-1 Vpr had half-lifes of 36 and 20 hr, respectively. Moreover, while both HIV-1 Vpr and HIV-2 Vpr cause cells to accumulate in G2 of the cell cycle, the effect of HIV-2 Vpr is attenuated relative to HIV-1 Vpr. Thus, protein stability correlates with both the function of Vpr and its virion incorporation.