Vpr Co-assembles with Gag during HIV-1 Assembly

The HIV-1 accessory protein Vpr is packaged into new virions at a 7:1 ratio of Gag/Vpr. Previous biochemical and genetic analysis has shown that Vpr gets packaged into virions via an LXXLF motif on the p6 domain of the Gag structural polyprotein. The kinetics of Vpr packaging compared to Gag assembly was previously unknown. Here, we confirm via biochemistry and imaging that fluorescently tagged Vpr gets packaged into virus-like particles only when the LXXLF motif is intact. When the LXXLF motif is mutated, Vpr is no longer recruited to Gag assemblies. When Vpr and Gag assembly are imaged together, we see that Vpr co-assembles with a slight delay compared to Gag suggesting that Vpr is not being recruited to the membrane with Gag but is instead being recruited to actively assembling Gag. ImportanceHIV-1 affects over 30 million people around the globe, and although we have good treatments, there is still no cure. The virus encodes 15 distinct proteins, and four of those proteins are known as accessory proteins. Vpr is one of the accessory proteins that is packaged into HIV-1 by interacting with the Gag structural protein. Without Vpr, HIV-1 is not as infectious. Our research shows that Vpr is packaged into new viruses as the virus is being formed rather than being put in towards the end of the assembly of a virus. Getting a clearer view of each step in the process of assembling each virion will help inform future treatments and help with overall comparisons between the assembly of different viruses.