Molecular biology
VIRION
Enveloped, brick-shaped virion, 250nm long and 200nm wide. The surface membrane displays surface tubules or surface filaments.
Two distinct infectious virus particles exists: the intracellular mature virus (IMV) and the extracellular enveloped virus (EEV).
Vaccinia virion 3D tour
GENOME
Linear, dsDNA genome of 170-250kb. The linear genome is flanked by inverted terminal repeat (ITR) sequences which form covalently closed hairpin termini at each extremity.
Vaccinia virus strain Western Reserve genome at Poxvirus Bioinformatics Resource center
GENE EXPRESSION
REPLICATION
CYTOPLASMIC
- Virus attaches to glycosaminoglycans (GAGs) on the surface of the target cell or by components of the extracellular matrix, triggering membrane fusion and release of the virus core into the cytoplasm.
- Early phase: early genes are transcribed in the cytoplasm by viral RNA polymerase. Early expression begins at 30 minutes post-infection.
- Core is completely uncoated as early expression ends, viral genome is now free in the cytoplasm.
- Intermediate phase: Intermediate genes are expressed, triggering genomic DNA replication at approximately 100 minutes post-infection. Genomic DNA becomes nicked and replication occurs through strand displacement synthesis with formation of genome concatemers.
- Late phase: Late genes are expressed from 140 min to 48 hours post-infection, producing all structural proteins.
- Assembly of progeny virions starts probably in association with internal membranes of the infected cell, producing an spherical immature particle. This virus particle matures into brick-shaped intracellular mature virion (IMV).
- IMV virion can be released upon cell lysis, or can acquire a second double membrane from trans-Golgi and bud as external enveloped virion (EEV)