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Transmission electron micrograph of polyomavirus SV40

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There are four polyomaviruses found in humans: JC virus, which can infect the respiratory system, kidneys, or brain (sometimes causing the fatal progressive multifocal leukoencephalopathy in the latter case), and BK virus, which produces a mild respiratory infection and can affect the kidneys of immunosuppressed transplant patients. Both viruses are very widespread: approximately 80 percent of the adult population in the United States have antibodies to BK and JC. Two recently discovered polyomaviruses, KI (Karolinska Institute)[1] and WU (Washington University)[2] viruses, are closely related to each other and have been isolated from respiratory secretions.

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.


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 derives from three abbreviations: Pa for Papillomavirus, Po for Polyomavirus, and Va for "vacuolating".


Prior to genome replication, the processes of viral attachment, entry and uncoating occur. Cellular receptors for polyomaviruses are currently unknown, however, attachment of polyomaviruses to host cells is mediated by viral protein 1 (VP1). This can be confirmed as anti-VP1 antibodies have been shown to prevent the binding of polyomavirus to host cells.[3]

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.





Release of newly synthesized polyomavirus particles exit the infected cell by one of two mechanisms. Firstly and less commonly, they are transported in cytoplasmic vacuoles to the plasma membrane, where budding ocurs. More frequently, they are released when the cell lyses due to the cytotoxicity of virus particles present in the infected cell.

The Polyoma Middle T-Antigen

The Polyoma Middle T-Antigen is used in animal breast cancer model systems like the PYMT system where it ist coupled to the MMTV promotor. There it functions as an oncogene, while the tissue where the tumor develops is determined by the MMTV promotor.

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