Histone H2A Ubiquitination Mediates the Establishment of Reactivation-Competent HSV-1 Latent Infection

Herpes simplex virus 1 (HSV-1) establishes a latent infection of neurons, where it persists for life with the capability to reactivate. During latent infection, heterochromatin is deposited onto the viral genome to presumably permit viral gene silencing. Repressive histone modifications associated with the latent genome include the constitutive heterochromatin modifications, H3K9me2/3, and the facultative heterochromatin modification, H3K27me3. The role of these different types during entry into latency and as substrates for reactivation is unknown. H3K27me3 is associated with Polycomb silencing, and a second modification also associated with Polycomb silencing, especially in pluripotent cells and during early development, is H2AK119ub1. Here we found that H2AK119ub1 is enriched on a sub-population of latent HSV genomes. We examined the contribution of both H2AK119ub1 and H3K7me3 deposition to HSV-1 gene silencing during entry into latency. We found that H2AK119ub1 was deposited prior to H3K27me3 and that only inhibition of H2AK119ub1 deposition plays a subtle role in latency establishment. Importantly, we found that inhibiting the enzymatic activity of Polycomb Repressive Complex 1 (PRC1) that deposits H2AK119ub1 during latency establishment prevented later reactivation. In contrast, inhibiting the activity of PRC2, which deposits H3K27me3, did not impact reactivation. Together, these data demonstrate the heterogenic nature of the epigenetic structure of latent HSV genomes and provide evidence that those associated with H2AK119ub1 are the template for reactivation.