Structural basis for HIV-1 Rev recognition by the histone chaperone human Nap1.

Human Nap1 (hNap1) is a histone chaperone involved in chromatin dynamics and has been shown to interact with the HIV-1 regulatory protein Rev, which is essential for nuclear export of viral RNA. Despite the functional significance of this interaction, its structural basis has remained elusive. Here, we present the X-ray crystal structure of hNap1 and the cryo-electron microscopy structure of the core domain of hNap1-Rev complex. The structure reveals that hNap1 binds Rev dimers via its acidic concave surface, engaging the Rev arginine-rich motif and oligomerization domain, and stabilizes Rev as a dimer-of-dimers tetramer. This interaction prevents higher-order Rev aggregation and enhances Rev's cooperative binding to the Rev Response Element. Surface plasmon resonance measurements confirm the formation of a stable complex with an apparent low-micromolar affinity between hNap1 and Rev, supporting a chaperone-like, reversible association. Our findings provide molecular insight into how hNap1 modulates Rev assembly and function, suggesting a model in which hNap1 primes Rev for productive engagement with viral RNA, thereby facilitating HIV-1 replication.