ICTV Virus Taxonomy Profile: Polyomaviridae

1LTAg, large T-antigen.

2Virions are typically 40–45 nm in diameter and lack an envelope. The icosahedral capsid is constituted of 72 capsomers, each composed of five molecules of the major capsid protein VP1 (Table 1, Fig. 1). Minor capsid proteins are located at the internal face of the capsid.

3The circular, dsDNA genome of approximately 5 kbp is packed with cellular histones and divided into three functional domains: the early region encoding regulatory proteins, the late region encoding capsid proteins, and the non-coding control region, which contains the origin of DNA replication and the promoter/enhancer elements directing transcription of the viral genes (, Fig. 2).

4Well-studied mammalian polyomaviruses require cellular glycans as host cell receptors. Viral decapsidation initiates in the cytosol and is completed in the nucleus, where replication and assembly occur. Viral transcription synthesizes a single precursor mRNA that is alternatively spliced to generate the major early proteins large T-antigen (LTAg) and small t-antigen (STAg), in addition to minor alternative proteins. LTAg of most polyomaviruses binds repeats of the 5′-GRGGC-3′ motifs, while LTAg of gammapolyomaviruses interacts with the palindromic motif 5′-CC(W)6GG-3′. LTAg possesses ATPase/helicase activity, and autoregulates transcription of the early genes. After replication has initiated, two major late transcripts are produced that are translated as the capsid proteins VP1 and VP2. Alternative start codon usage of the VP2 mRNA can produce VP3. Avian polyomaviruses possess a unique VP4 capsid protein, and some mammalian polyomaviruses produce an agnoprotein that is involved in transcription, virus maturation and egress. Mature virions are released by cell lysis or non-lytically. Polyomavirus infection can be symptomatic and may cause severe disease, including malignancy and organ failure, resulting in death.

5This genus includes >30 species. Members infect humans and other mammals. Merkel cell polyomavirus and raccoon polyomavirus are so far the only members known to cause cancer in their natural host.

6This genus includes >20 species. Members infect mammals. The well-studied human polyomaviruses BK and JC are associated with nephropathy and progressive multifocal leukoencephalopathy, respectively.

7This genus includes <10 species. Members infect birds. Some cause severe illness and even death, but oncogenicity has not been observed.

8This genus includes the species Human polyomavirus 6 and Human polyomavirus 7, members of which exhibit skin tropism, and Human polyomavirus 10 and Human polyomavirus 11, members of which (MW polyomavirus and STL polyomavirus, respectively), are commonly detected in the gastrointestinal tract.

9The general mode of polyomavirus diversification is co-speciation with their hosts. Recombination has shaped polyomavirus genomes and resulted in conflicting phylogenetic signals from the early and late genomic regions. A distant evolutionary relationship of polyomaviruses to ssDNA viruses has been suggested on the basis of structural similarity in replicative proteins.

10Full ICTV Online (10th) Report: www.ictv.global/report/polyomaviridae.