During latent infections with herpes simplex virus 1 (HSV-1), viral transcription is restricted and the genomes are mostly maintained in silenced chromatin, whereas in lytically infected cells all viral genes are transcribed and the genomes are dynamically chromatinized. Histones in the viral chromatin bear markers of silenced chromatin at early times in lytic infection or of active transcription at later times. The virion protein VP16 activates transcription of the immediate-early (IE) genes by recruiting transcription activators and chromatin remodelers to their promoters. Two IE proteins, ICP0 and ICP4 which modulate chromatin epigenetics, then activate transcription of early and late genes. Although chromatin is involved in the mechanism of activation of HSV- transcription, its precise role is not entirely understood. In the cellular genome, chromatin dynamics often modulate transcription competence whereas promoter-specific transcription factors determine transcription activity. Here, biophysical fractionation of serially digested HSV-1 chromatin followed by short-read deep sequencing indicates that nuclear HSV-1 DNA has different biophysical properties than protein-free or encapsidated HSV-1 DNA. The entire HSV-1 genomes in infected cells were equally accessible. The accessibility of transcribed or non-transcribed genes under any given condition did not differ, and each gene was entirely sampled in both the most and least accessible chromatin. However, HSV-1 genomes fractionated differently under conditions of generalized or restricted transcription. Approximately 1/3 of the HSV-1 DNA including fully sampled genes resolved to the most accessible chromatin when HSV-1 transcription was active, but such enrichment was reduced to only 3% under conditions of restricted HSV-1 transcription. Short sequences of restricted accessibility separated genes with different transcription levels. Chromatin dynamics thus provide a first level of regulation on HSV-1 transcription, dictating the transcriptional competency of the genomes during lytic infections, whereas the transcription of individual genes is then most likely activated by specific transcription factors. Moreover, genes transcribed to different levels are separated by short sequences with limited accessibility.
Conflict of interest statement
The authors have declared that no competing interests exist.
Chromatin Dynamics During Lytic Infection With Herpes Simplex Virus 1KL Conn et al. Viruses 5 (7), 1758-86. PMID 23863878. - ReviewLatent HSV-1 genomes are chromatinized with silencing marks. Since 2004, however, there has been an apparent inconsistency in the studies of the chromatinization of the H …
VP16-dependent Association of Chromatin-Modifying Coactivators and Underrepresentation of Histones at Immediate-Early Gene Promoters During Herpes Simplex Virus InfectionFJ Herrera et al. J Virol 78 (18), 9689-96. PMID 15331701.During infection by herpes simplex virus type 1 (HSV-1), the virion protein VP16 activates the transcription of viral immediate-early (IE) genes. Genetic and biochemical …
An Essential Viral Transcription Activator Modulates Chromatin DynamicsRL Gibeault et al. PLoS Pathog 12 (8), e1005842. PMID 27575707.Although ICP4 is the only essential transcription activator of herpes simplex virus 1 (HSV-1), its mechanisms of action are still only partially understood. We and others …
Repression of Gene Expression Upon Infection of Cells With Herpes Simplex Virus Type 1 Mutants Impaired for Immediate-Early Protein SynthesisCM Preston et al. J Virol 71 (10), 7807-13. PMID 9311867.Herpes simplex virus type 1 (HSV-1) mutants defective in immediate-early (IE) gene expression do not readily enter productive replication after infection of tissue cultur …
Early Expression of Herpes Simplex Virus (HSV) Proteins and Reactivation of Latent InfectionJ Rajcáni et al. Folia Microbiol (Praha) 45 (1), 7-28. PMID 11200675. - ReviewDuring the last decade, new data accumulated describing the early events during herpes simplex virus 1 (HSV-1) replication occurring before capsid formation and virion en …