Open reading frame vpr of simian immunodeficiency virus encodes a virion-associated protein

The genomes of simian immunodeficiency viruses isolated from rhesus macaques (SIV_mac) contain an open reading frame (ORF), vpr, which has a coding potential of 97 to 101 amino acid residues. In this study, a vpr ORF-encoded protein of approximately 11 kDa was identified, and anti-vpr antibodies were detected in rhesus macaques infected by SIV_mac. These results provide clear evidence that the vpr ORF is a coding gene of SIV_mac. The vpr protein, like the vpx protein which is encoded by another accessory gene of SIV_mac, was also found to be associated with viral particles. This observation demonstrates that more than one accessory gene product can be present in the virions of this family of retroviruses and raises the possibility that the vpr protein may have a role in early part of the virus life cycle.