Molecular biology

VIRION

Non-enveloped, round, icosahedral symmetry (T=1), 21-22 nm in diameter. The capsid consists of 60 copies of CP protein.

GENOME

Linear, single-stranded DNA of about 4kb in size, with long inverted terminal repeats. both positive and negative strand are encapsidated, but majority is of negative polarity (85%).
The genome is replicated through rolling-hairpin mechanism.

GENE EXPRESSION

Host proteins transcribe the genomes into mRNAs.

REPLICATION

NUCLEAR

1. Virus penetrates into the host cell.
2. Uncoating, and release of the viral genomic ssDNA into the nucleus.
3. The ssDNA is converted into dsDNA by cellular proteins.
4. viral mRNAs are transcribed when host cell enters S phase and translated to produce viral proteins.
5. Replication occurs through rolling-hairpin mechanism, with NS1 nickase binding covalently to the 5’ genomic end.
6. Individual ssDNA genomes are excised from replication concatemers by a process called junction resolution.
7. These newly synthesized ssDNA can either
   a) be converted to dsDNA and serve as a template for transcription/replication
   b) be encapsidated to form new virions that can bud out of the host cell.