A conserved dileucine-containing motif in p6gag governs the particle association of Vpx and Vpr of simian immunodeficiency viruses SIVmac and SIVagm

Vpr is a small accessory protein of human and simian immunodeficiency viruses (HIV and SIV) that is specifically incorporated into virions. Members of the HIV-2/SIVsm/SIVmac lineage of primate lentiviruses also incorporate a related protein designated Vpx. We previously identified a highly conserved L-X-X-L-F sequence near the C terminus of the p6 domain of the Gag precursor as the major virion association motif for HIV-1 Vpr. In the present study, we show that a different leucine-containing motif CD-X-A-X-X-L-LI in the N-terminal half of p6(gag) is required for the incorporation of SIVmac Vpx. Similarly, the uptake of SIVmac Vpr depended primarily on the D-X-A-X-X-L-L motif. SIVmac Vpr was unstable when expressed alone, but its intracellular steady-state levels increased significantly in the presence of wild-type Gag or of the proteasome inhibitor lactacystin. Collectively, our results indicate that the interaction with the Gag precursor via the D-IC-A-X-XL-L motif diverts SIVmac Vpr away from the proteasome-degradative pathway. While absent from HIV-1 p6(gag), the D-X-A-X-X-L-L motif is conserved in both the HIV-2/SIVsm/SIVmac and SIVagm lineages of primate lentiviruses. We found that the incorporation of SIVagm Vpr, like that of SIVmac Vpx, is absolutely dependent on the D-X-A-X-X-L-L motif, while the L-X-X-L-F motif used by HIV-1 Vpr is dispensable. The similar requirements for the incorporation of SIVmac Vpx and SIVagm Vpr provide support for their proposed common ancestry.