Molecular biology
VIRION
Non-enveloped, round, icosahedral symmetry (T=1), 18-26 nm in diameter. The capsid consists of 60 copies of CP protein.
GENOME
Linear, single-stranded DNA of about 4 to 6 kb in size.
The genome is replicated through rolling-hairpin mechanism.
GENE EXPRESSION
Host proteins transcribe the genomes into mRNAs. Depending of the virus there can be one (Erythrovirus and Iteravirus), two (Densovirus and Brevidensovirus) or three (Dependovirus) promoters for mRNA transcription. Some mRNAs are spliced allowing alternative forms of the protein to be produced.
REPLICATION
NUCLEAR
- Virus penetrates into the host cell.
- Uncoating, and release of the viral genomic ssDNA into the nucleus.
- The ssDNA is converted into dsDNA by cellular proteins.
- viral mRNAs are transcribed when host cell enters S phase and translated to produce viral proteins.
- Replication occurs through rolling-hairpin mechanism, whith NS1 nickase binding covalently to the 5’ genomic end.
- Individual ssDNA genomes are excised from replication concatemers by a process called junction resolution.
- 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 budd out of the host cell.