Molecular biology
VIRION
Enveloped, spherical to pleomorphic, 150-200 nm in diameter, T=16 icosahedral symmetry. Capsid consists of 162 capsomers and is surrounded by an amorphous tegument.
GENOME
Monopartite, linear, dsDNA genome of 152 kb. The genome contains terminal and internal reiterated sequences.
GENE EXPRESSION
All genes are transcribed by the host RNA polymerase II., and most mRNA are unspliced. There are three temporal classes of genes: immediate-early (alpha), early (beta) and late (gamma). The immediate-early genes are transcribed immediately after infection to take control of cell defense and to activate early genes. These encode the proteins necessary for the viral DNA replication. The late genes mostly encode structural proteins. Latent genes can stop the replicative process at the early step
The viral proteins VHS and ICP27 are involved in shut-off of host protein translation in order to ensure the selective expression of viral proteins versus cellular proteins.
REPLICATION
NUCLEAR
Lytic replication:
- Virus attaches to host receptors through gB, gC, gD and gH .
- Fusion with the plasma membrane to release the core and the tegument proteins into the host cytoplasm.
- The capsid is transported to the nuclear pore where the viral DNA is released into the nucleus.
- Transcription of immediate early mRNA by host polymerase II, that will in turn activate early genes.
- Transcription of early viral mRNA by host polymerase II.
- Synthesis of multiple copies of viral DNA by the viral DNA-dependent DNA polymerase, followed by the activation of late genes.
- Transcription of late genes, comprising mainly structural and virion exit proteins.
- Capsid is assembled into the nucleus around scaffold proteins. The replicated DNA
- Assembly of the virus and budding through the inner lamella of the nuclear membrane which has been modified by the insertion of herpes glycoproteins, throughout the Golgi and final release at the plasma membrane.
Latent replication : replication of circular viral episome in tandem with the host cell DNA using the host cell replication machinery.