Polyomaviridae

The Polyomaviridae family includes non-enveloped DNA viruses that result in different vertebrates (mammals, rodents and birds) and humans to persistent infections. The family is monotypic, ie, there is currently only one genus polyomavirus. This genus has emerged from the obsolete today Papovaviridae family. The name of the family is composed of the Greek πολύς ( poly: much more ) and the suffix -oma from the name for tumors, since the first identified virus of the family, which, in newborn mice results in murine polyomavirus at different tumors.

Morphology

Virions of polyomaviruses consist of a bare, about 40 to 45 nm in diameter major capsid is composed of 72 capsomeres. Capsomeres which are arranged in an icosahedral symmetry (T = 7). The individual capsomeres are formed on the basis of five molecules of the capsid protein VP1 ( pentamer ), but not to each other uniformly, but rotated ( skewed ) are arranged. It is also described by a twisted, icosahedral symmetry (T = 7d). On the inside of Kapids capsid proteins VP2 and VP3 stabilize the VP1 backbone; They also interact with the dsDNA in the interior of the capsid. Often different virus particles are observed, including empty capsids normally structured, very small, empty capsids ( Mikrokapside ) and irregular tubular structures, which are formed from the capsid proteins of varying composition. The VP1 capsid protein can self-assemble without further viral proteins spontaneously into virus - like particles, but can pack no nucleic acid. In real virion VP1 accounts for about 70% of the total protein content.

Inside the capsid is the covalently closed circle of DNA of the virus genome. This is. Like the Papillomaviridae multiple twisted ( " supercoiled " ) and together with a nucleoprotein cellular histones, which are structurally very similar to the eukaryotic nucleosomes Of the five known histones are found the histones H2A, H2B, H3 and H4.

The capsids are very environmentally stable and can not be inactivated with diethyl ether, 2- propanol or detergents ( soap). They are heat stable up to 50 ° C for 1 hour; while the presence of magnesium chloride in 1 M concentration, are unstable capsids, suggesting similar to the dependence of the papillomavirus capsid of divalent cations.

Genome

The genome of the polyoma viruses consists of a single molecule of double-stranded, covalently closed DNA ring. Starting from a non-coding, regulatory region, the open reading frames (ORFs ) of the different viral proteins of 5 to 9 are arranged so that the ORFs of the early transcripts in a reading direction running in the opposite direction. Late transcripts One of the early transcripts include the large and possibly small T antigen and other regulatory proteins; the late transcripts encoding the three structural proteins VP1 - third The reading frame overlap with partially different reading frames, so that the polyomaviruses encode with a genome size of about 4.7 to 5.5 kbp for a relatively high number of proteins. As the papillomaviruses have the polyomaviruses not have its own DNA polymerase for replication of viral DNA, they are also dependent on the cell's own polymerases. The early viral proteins bind to the enhancers and promoters for their own reading frames in the regulatory region. Thus, the production of these proteins in favor of late proteins is suppressed in the course of virus multiplication. The study of this mechanism in the SV -40 led to the discovery of these regulatory sequences in eukaryotes and development of the enhancer concept in molecular biology.

Biological Significance

Avian polyomaviruses solve, for example, the French moult. The BK virus ( BKV, BK polyomavirus or BKPyV ) can cause in humans with immunosuppressive treatment after kidney transplantation in the loss of the graft. The BK virus can also cause children to respiratory infection or cystitis, it can be a hemorrhagic cystitis in bone marrow transplant patients, a ureteral stenosis in kidney transplant patients and meningoencephalitis in AIDS patients cause.

Belonging to the genus BK and JC viruses, which are now referred to as polyoma virus hominis type 1 and 2, persist in the kidney tissue; in the normal population antibodies against BK virus can be detected at 100% and against JC virus to about 80%.

The fact that in not substantially pre humans and in absence of any double infection or secondary infection is an infection with these viruses only extremely rarely takes a fatal course, indicates firstly that these disease-causing viruses are highly adapted to humans as its reservoir host. The damage to his reservoir host is not advantageous effect of a virus because it is for their own propagation rely on this. The triggered yet of this virus in the reservoir host disease are ultimately only side effects of the infection. Second, is also evident that the man also in the course of many generations could adapt to this virus. There is currently a BK virus infection rate of the population of 80-90 %. JC virus ( JCV ) results in cellular immunosuppressed (AIDS St. C3 ) for progressive multifocal leukoencephalopathy (PML ). The PML is almost always fatal.

The Simiane Virus 40 or SV40 is a potential trigger for various tumor diseases. Parts of the SV40 DNA found in molecular biology application as a particularly strong promoter or enhancer.

System

• Family Polyomaviridae

• Genus polyomavirus

• Species monkeys polyomavirus ( AGMPyV )
• Species baboon polyomavirus 2 ( BPYV -2)
• Human polyomavirus species 1 ( BK virus, BKV or BKPyV )
• Human polyomavirus species 2 ( JC virus, JCV or JCPyV )
• Species Bovine polyomavirus ( BPYV )
• Species budgerigar polyomavirus ( polyomavirus nestling disease of budgerigars, BFPyV )
• Species hamster polyomavirus ( HaPyV )
• Species Murine Pneumotropes virus ( MPTV )
• Species Murine polyomavirus ( MPyV )
• Species rabbit polyomavirus (Rabbit kidney vacuolating virus, RKV)
• Species Simian Virus 12 (SV -12)
• Species Simian Virus 40 (SV -40)

• Species crow polyomavirus
• Haemorrhagic polyomavirus species of geese ( GHPV )
• Species Merkel cell polyomavirus
• Species chimpanzee polyomavirus
• Species finch polyomavirus
• Species KI polyomavirus ( KIV)