Vpr, a 96 amino acid 14-kDa protein, plays an important role in regulating nuclear import of the HIV-1 pre-integration complex, and is required for virus replication and enhanced gene expression from provirus in dividing or non-dividing cells such as T cells or macrophages.

[6] VprBP acts as a substrate-recognition unit when associated with DNA damage-binding protein 1 (DDB1) as part of a CUL4–DDB1 E3 ubiquitin ligase complex.

p53 is an important tumor suppressor which induces either cell cycle arrest or apoptosis in response to DNA damage.

These findings suggest that the evolutionarily secured G2 cell cycle arrest function of Vpr (Viral Protein R) is essential for HIV-1 replication.

Furthermore, this innovative in-vitro culture system will allow researchers to address mechanisms underlying Vpr-mediated enhancement of HIV-1 replication.