ATRX promotes transcription initiation of HSV-1 immediate early genes [ATRX ChIP-seq]

Herpes simplex virus 1 (HSV-1) transcribes its genome in a highly coordinated temporal cascade, utilizing the host RNA polymerase II (Pol II). Repression of transcription precedes the cascade's progression in a process requiring viral immediate early (IE) genes, in a phenomenon termed Transient Immediate Early gene Mediated Repression (TIEMR). Given that components of promyelocytic leukaemia nuclear bodies (PML-NBs) are known to rapidly engage incoming HSV-1 genomes, we investigated their potential role in TIEMR regulation. Using siRNA knockdown of PML-NB constituents (PML, DAXX, and ATRX), we unexpectedly observed that ATRX depletion resulted in a significant reduction in nascent viral transcription on viral IE promoters at 1.5 hours post-infection (hpi). ChIP-Seq analysis indicated ATRX is associated with both highly transcriptionally active and transcriptionally restricted regions, indicating that ATRX has diverse functions in the viral genome. We show here that ATRX association with active transcription on IE genes is correlated to the presence of G-quadruplexes (G4s). Drug stabilization of G4s mimicked the effects of ATRX knockdown, significantly reducing transcription initiation on IE genes. These findings suggest that ATRX promotes transcriptional initiation of HSV-1 IE genes by preventing G4 formation. In sum, our results reveal a previously unrecognized pro-transcriptional role for ATRX early in HSV-1 infection.