Molecular biology

VIRION

Non-enveloped, round, icosahedral symmetry (T=1), about 30 nm in diameter. The capsid consists of 12 pentagonal trumpet-shaped pentomers. The virion is composed of 60 copies each of the F, G, and J proteins, and 12 copies of the H protein. There are 12 spikes which are each composed of 5 G and one H proteins.

GENOME

Circular, single-stranded DNA of 4.4 to 6.1kb. replication occurs via dsDNA intermediate and rolling circle.

GENE EXPRESSION

Early and late genes promoters tightly regulates the timing of gene expression, which is crutial for the replication cycle.

REPLICATION

CYTOPLASMIC

1. Virus particle binds to target cell.
2. The proteins of the capsid inject the DNA core into cell cytoplasm.
3. Host polymerase convert the (+)ssDNA viral genome into a covalently closed dsDNA called replicative form DNA I (RFI).
4. Early viral genes are transcribed by host RNA polymerase, producing viral replication proteins.
5. Viral protein A cleaves RFI DNA strand at the origin of replication and covalently attaches itself to the DNA, generating RFII molecule.
6. (+)strand replication occurs by rolling circle, which is converted to dsDNA by host polymerase.
7. Late viral genes are transcribed by host RNA polymerase.
8. Procapsid assembly in the cytoplasm.
9. Viral protein C binds to replication complex, inducing packaging of neo-synthesized (+)DNA into procapsids.
10. Procapsids are matured in host cytoplasm
11. Viral lysozyme attacks the peptidoglycan wall, lysing the cell and releasing mature virions.