Molecular biology
VIRION
Non-enveloped, round, icosahedral symmetry (T=1), about 17 nm in diameter. The capsid consists of 12 pentagonal trumpet-shaped pentomers.
GENOME
Monopartite, circular, single-stranded DNA of about 1800 to 2000bp.
The genome is replicated through double-stranded intermediates. The replication (Rep) protein initiates and terminates rolling-circle replication, the host DNA polymerase being used for DNA replication itself. There is a potential stem-loop structure in the intergenic region that includes a conserved nonanucleotide sequence (AGTATTAC) where ssDNA synthesis is initiated.
GENE EXPRESSION
The genome is ambisense. The encapsidated viral DNA and the complementary DNA of the replicative intermediate encode two mRNAs for the Rep and capsid proteins.
Rep mRNA can be spliced in some strains to produce Rep’ protein.
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 with the participation of cellular factors.
- viral mRNAs are transcribed and translated to produce viral proteins.
- Replication may be mediated by a “Rep-like” protein, and would occur by rolling circle producing ssDNA genomes
- These newly synthesized ssDNA can either
a) be converted to dsDNA and serve as a template for transcription/replication
b) be encapsidated by capsid protein and form virions released from the cell by budding