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Polyomavirus is the sole genus of viruses within the family Polyomaviridae. Polyomaviruses are DNA-based (double-stranded DNA,~5000 base pairs,circular genome), small (40-50 nanometers in diameter), and icosahedral in shape, and do not have a lipoprotein envelope. They are potentially oncogenic (tumor-causing); they often persist as latent infections in a host without causing disease, but may produce tumors in a host of a different species, or a host with an ineffective immune system. The name polyoma refers to the viruses’ ability to produce multiple (poly-) tumors (-oma).
The genus Polyomavirus used to be one of two genera within the now obsolete family Papovaviridae (the other genus being Papillomavirus which is now assigned to its own family Papillomaviridae). The name Papovaviridae derived from three abbreviations: Pa for Papillomavirus, Po for Polyomavirus, and Va for “vacuolating”.
Five polyomaviruses have been found in humans.
The Simian vacuolating virus 40 replicates in the kidneys of monkeys without causing disease, but causes sarcomas in hamsters. It is unknown whether it can cause disease in humans, which has caused concern since the virus may have been introduced into the general population in the 1950s through a contaminated polio vaccine.
An avian polyomavirus sometimes referred to as the Budgerigar fledgling disease virus is a frequent cause of death among caged birds.
Prior to genome replication, the processes of viral attachment, entry and uncoating occur. Cellular receptors for polyomaviruses are sialic acid residues of gangliosides. The attachment of polyomaviruses to host cells is mediated by viral protein 1 (VP1) via the sialic acid attachment region. This can be confirmed as anti-VP1 antibodies have been shown to prevent the binding of polyomavirus to host cells.[1]
Polyomavirus virions are subsequently endocytosed and transported directly to the nucleus in endocytic vacuoles where uncoating occurs.
Polyomaviruses replicate in the nucleus of the host. They are able to utilise the host’s machinery because the genomic structure is homologous to that of the mammalian host. Viral replication occurs in two distinct phases; early and late gene expression, separated by genome replication.
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