Herpes simplex virus 1 (HSV-1) establishes
latent infection in neurons via a variety of epigenetic mechanisms that silence its genome. The cellular
CCCTC-binding factor (CTCF) functions as a mediator of transcriptional control and
chromatin organization and has binding sites in the HSV-1 genome. We constructed an HSV-1 deletion mutant that lacked a pair of CTCF-binding sites (CTRL2) within the latency-associated transcript (LAT) coding sequences and found that loss of these CTCF-binding sites did not alter lytic replication or levels of establishment of
latent infection, but their deletion reduced the ability of the virus to reactivate from
latent infection. We also observed increased
heterochromatin modifications on viral
chromatin over the LAT promoter and intron. We therefore propose that CTCF binding at the CTRL2 sites acts as a
chromatin insulator to keep viral
chromatin in a form that is poised for reactivation, a state which we call poised latency.IMPORTANCE Herpes simplex virus 1 (HSV-1) is a human pathogen that persists for the lifetime of the host as a result of its ability to establish
latent infection within sensory neurons. The mechanism by which HSV-1 transitions from the lytic to
latent infection program is largely unknown; however, HSV-1 is able to coopt cellular silencing mechanisms to facilitate the suppression of lytic gene expression. Here, we demonstrate that the cellular
CCCTC-binding factor (CTCF)-binding site within the latency associated transcript (LAT) region is critical for the maintenance of a specific local
chromatin structure. Additionally, loss of CTCF binding has detrimental effects on the ability to reactivate from
latent infection. These results argue that CTCF plays a critical role in epigenetic regulation of viral gene expression to establish and/or maintain a form of
latent infection that can reactivate efficiently.