Human immunodeficiency virus vpr gene encodes a virion-associated protein

The vpr gene of human immunodeficiency virus type 1 (HIV-1) is one of the seven accessory genes that are believed to have roles in the virus replication cycle. We report here the detection of a 13 kD vpr protein in sucrose gradient-purified HIV-1. This protein was not detected in cells infected with a virus having a truncated vpr gene that lacks the potential to encode for 26 C-terminal amino acid residues. These findings raise the possibility that virion-associated vpr proteins may be involved in the early life cycle of HIV-1 replication and suggest that the C-terminal region of the vpr gene is essential for its expression.