Background: The formation of new infectious human immunodeficiency type 1 virus (HIV-1) mainly relies on the homo-multimerization of the viral structural polyprotein Pr55Gag and on the recruitment of host factors. We have previously shown that the double-stranded RNA-binding protein Staufen 1 (Stau1), likely through an interaction between its third double-stranded RNA-binding domain (dsRBD3) and the nucleocapsid (NC) domain of Pr55Gag, participates in HIV-1 assembly by influencing Pr55Gag multimerization.
Results: We now report the fine mapping of Stau1/Pr55Gag association using co-immunoprecipitation and live cell bioluminescence resonance energy transfer (BRET) assays. On the one hand, our results show that the Stau1-Pr55Gag interaction requires the integrity of at least one of the two zinc fingers in the NC domain of Pr55Gag but not that of the NC N-terminal basic region. Disruption of both zinc fingers dramatically impeded Pr55Gag multimerization and virus particle release. In parallel, we tested several Stau1 deletion mutants for their capacity to influence Pr55Gag multimerization using the Pr55Gag/Pr55Gag BRET assay in live cells. Our results revealed that a molecular determinant of 12 amino acids at the N-terminal end of Stau1 is necessary to increase Pr55Gag multimerization and particle release. However, this region is not required for Stau1 interaction with the viral polyprotein Pr55Gag.
Conclusion: These data highlight that Stau1 is a modular protein and that Stau1 influences Pr55Gag multimerization via 1) an interaction between its dsRBD3 and Pr55Gag zinc fingers and 2) a regulatory domain within the N-terminus that could recruit host machineries that are critical for the completion of new HIV-1 capsids.