| Herpes simplex virus type 1 (HSV-1) genomes associate with histones in unstable nucleosomes during lytic infections. Nucleosome core particles are 146 base pairs of DNA wrapped around a histone octamer of two molecules of each H2A, H2B, H3, and H4. Histone H1 binds to nucleosomes at DNA entry and exit points. Association with histones is proposed to regulate HSV-1 gene expression. Consistently, HSV-1 transcription transactivators disrupt chromatin and HSV-1 strains mutant in these transactivators are replication impaired or transcriptionally inactive.;Histones in cellular chromatin normally disassociate, diffuse through the nucleus, and re-associate at different sites. I propose that histones are mobilized from domains of cellular chromatin to those domains containing HSV-1 genomes in cellular attempts to silence HSV-1 gene expression. I additionally propose that HSV-1 further mobilizes histones to counteract such silencing attempts. My hypothesis is that histones are mobilized during HSV-1 infection.;In this thesis, I show that linker and core histones are mobilized during HSV-1 infection. Such mobilization results in increases to their "free" (not bound to chromatin) pools. Linker and core histones were mobilized even when HSV-1 proteins were not expressed, mobilization that likely reflects cellular responses to infection. Histone mobilization was enhanced when HSV-1 IE or E proteins were expressed. This enhanced mobilization was independent of HSV-1 DNA replication and late proteins. Core histones H2B and H3.3 were differentially mobilized, suggesting that different mechanisms may mobilize histones during HSV-1 infection.;My discovery of histone mobilization reveals a novel consequence of cell-virus interactions that addresses a previously unexplained aspect of HSV-1 infection.;HSV-1 genomes have dynamic associations with histones. The genomes are not associated with histones in capsids, and input genomes are delivered to nuclear domains depleted of histones. Later during infection, HSV-1 genomes again occupy nuclear domains depleted of histones. Histone synthesis is inhibited during infection and the total level of nuclear histones remains relatively constant. It is therefore unlikely that the histones that first bind to HSV-1 genomes are newly synthesized. The source of the histones that associate with HSV-1 genomes has yet to be addressed. |
