Alphapolyomavirus (taxid:1891713)

VIRION

Non-enveloped capsid with a T=7d icosahedral symmetry, about 50 nm in diameter.

GENOME

Circular dsDNA about 5 kb in size, associated with cellular histones in a chromatin-like complex. Encodes for 5-6 proteins.

GENE EXPRESSION

Transcription is nuclear, in two phases; early (replication), late (virion assembly/exit). 5-6 proteins are expressed from the two pre-MRNA by alternative splicing. All genes are transcribed by host RNA pol II.

REPLICATION

NUCLEAR

1. Attachement of the viral proteins to host receptors triggers lipid-mediated endocytosis of the virus into the host cell.
2. Virion transits through endoplasmic reticulum where host protein disulfide isomerases rearrange its capsid structure
3. Export of misfolded virion to the cytoplasm possibly through host ERAD pathway
4. Loss of VP1 in the low-calcium conditions of the cytosol
5. Import of genomic DNA into host nucleus.
6. Transcription of early genes (LT and sT genes)
7. Replication of the DNA genome in the nucleus.
8. Transcription of late genes encoding for structural proteins (VP1, VP2 and VP3).
9. Assembly of new virions in nuclear viral factories.
10. Virions are released by lysis of the cell.