The HSV-1 LAT enhancer regulates locus-specific H3.1 enrichment during early lytic infection

The Herpes Simplex Virus 1 (HSV-1) genome undergoes extensive chromatinization following entry into the nucleus, yet how viral regulatory elements influence this process during lytic infection remains poorly understood. The HSV-1 latency-associated transcript enhancer (LTE) is well established as a key element in the regulation of latency and reactivation, but its role during the productive infection has not been defined. Here, we identify a role for the LTE in regulating chromatin composition on the lytic HSV-1 genome. Deletion of a 310-bp region within the LTE selectively reduced enrichment of the canonical histone H3.1 at specific viral lytic genes, including ICP4 and ICP8, without altering H3.3 enrichment. This phenotype was not reproduced using a second LTE deletion that disrupted enhancer activity, indicating that regulation of H3.1 enrichment is separable from the function of the enhancer. LTE-dependent H3.1 enrichment persisted in the absence of viral DNA replication and was accompanied by reduced occupancy of the H3.1 histone chaperone CAF-1. However, depletion of CAF-1 did not substantially reduce H3.1 enrichment, indicating that additional mechanisms contribute to H3.1 association with the viral genome. Together, these findings reveal that the HSV-1 LTE regulates locus-specific chromatin composition during early lytic infection and identify a previously unrecognized connection between a viral enhancer and histone H3.1 enrichment on the incoming viral genome.

Viruses must organize their genetic material inside infected cells to control when viral genes are turned on and off. After HSV-1 enters a cell, its DNA becomes associated with histones. Although HSV-1 contains regulatory sequences that control viral gene expression, it is not well understood how these sequences influence the chromatin deposited on the viral genome during infection. In this study, we discovered that the HSV-1 enhancer (LTE), a viral DNA element previously known primarily for its role in latency and reactivation, also regulates the chromatin landscape during lytic infection. Removing a specific region of this enhancer reduced the association of H3.1 early after infection. This effect was also associated with decreased binding of the cellular histone-loading complex CAF-1. These changes in the chromatin landscape were accompanied by altered expression of specific viral genes. Together, our findings reveal an unexpected role for the LTE in regulating the chromatin environment of the viral genome during lytic infection and provide new insight into how viral DNA elements interact with cellular chromatin machinery to control infection.