Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
"Viral protein R" accelerates the production of HIV proteins.
It also facilitates the nuclear localisation of the preintegration complex - the agglomeration of viral RNA and reverse transcriptase and integrase proteins which must form in order for the HIV genome to be integrated into the host cell's genome. Vpr carries "nuclear localisation signals" (sequences of protein which are recognised by cellular machinery as indicating that it should be transported into the nucleus), and in a sense it mimicks the behaviour of a protein called importin-beta.
There also seems to be a role for Vpr in stopping the host cell going through the ordinary "cell cycle" - many cells normally go through a regular cycle of splitting to create new cells, but Vpr can stop host cells doing this. It seems that a cell which has been stopped during the so-called "G2" phase of the cell cycle is a nicer environment for HIV replication.