A Conserved Dileucine-Containing Motif in p6 gag Governs the Particle Association of Vpx and Vpr of Simian Immunodeficiency Viruses SIV mac and SIV agm

Abstract

ABSTRACT 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/SIV sm /SIV mac 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 (D-X-A-X-X-L-L) in the N-terminal half of p6 gag is required for the incorporation of SIV mac Vpx. Similarly, the uptake of SIV mac Vpr depended primarily on the D-X-A-X-X-L-L motif. SIV mac 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-X-A-X-X-L-L motif diverts SIV mac 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/SIV sm /SIV mac and SIV agm lineages of primate lentiviruses. We found that the incorporation of SIV agm Vpr, like that of SIV mac 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 SIV mac Vpx and SIV agm Vpr provide support for their proposed common ancestry.