ATRX Promotes Transcription Initiation of HSV-1 Immediate Early Genes During Early Lytic Infection

Herpes simplex virus 1 (HSV-1) transcribes its genome using host RNA polymerase II (Pol II) in a temporally regulated cascade. We previously proposed a model of Transient Immediate Early gene Mediated Repression (TIEMR), in which early repression of immediate early (IE) genes is relieved to initiate the cascade. Given the rapid association of promyelocytic leukaemia nuclear body (PML-NB) components with incoming HSV-1 genomes, we sought to investigate their roles in TIEMR. siRNA knockdown revealed that depletion of ATRX, but not PML, significantly reduced nascent transcription from viral IE promoters at 1.5 hpi, while DAXX knockdown increased transcription. ChIP-Seq showed ATRX localizes to both transcriptionally active IE genes and restricted non-IE genes, suggesting diverse functions. Notably, ATRX occupancy at active IE promoters correlated with G-quadruplex (G4) motifs, and G4 stabilization mimicked ATRX knockdown by reducing transcription initiation. These findings uncover a previously unrecognized pro-transcriptional role for ATRX at IE genes and suggest that ATRX promotes escape from TIEMR by facilitating transcription initiation and preventing G4-mediated repression.