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Teschovirus A Picornavirus is a virus belonging to the family Picornaviridae. Picornaviruses are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual because it has a protein on the 5' end that is used as a primer for transcription by RNA polymerase. The name is derived from pico meaning small, and RNA referring to the ribonucleic acid genome, so "picornavirus" literally means small RNA virus. Picornaviruses are separated into nine distinct genera and include many important pathogens of humans and animals.[1] The diseases they cause are varied, ranging from acute "common-cold"-like illnesses, to poliomyelitis, to chronic infections in livestock. Two main categories are enteroviruses and rhinoviruses. Picornaviruses are classed under Baltimore's viral classification system as group IV viruses as they contain a single stranded, positive sense RNA genome of between 7.2 and 9.0 kb in length. Like most positive sense RNA genomes, the genetic material alone is infectious; although substantially less virulent than if contained within the viral particle, the RNA can have increased infectivity when transfected into cells. The genome itself is the same sense as mammalian mRNA, being read 5’ to 3’. Unlike mammalian mRNA Picornaviruses do not have a 5’ CAP but a virally encoded protein known as VPg, however like mammalian mRNA the genome does have a poly A tail at the 3’ end. There is an un-translated region (UTR) at both ends of the Picornavirus genome. The 5’ UTR is longer, being around 600-1200 BP in length, compared to that of the 3’ UTR, which is around 50-100bp. It is thought that the 5’ UTR is important in translation and the 3’ in negative strand synthesis; however the 5’ end may also have a role to play in virulence of the virus. The rest of the genome encodes structural proteins at the 5’ end and non-structural proteins at the 3’ end in a single polyprotein. Experimental data from single step growth-curve-like experiments have allowed scientists to look at the replication of the picornaviruses in great detail. The whole of replication occurs within the host cell cytoplasm and infection can even happen in cells that do not contain a nucleus (known as enucleated cells) and those treated with actinomycin D (this antibiotic would inhibit viral replication if this occurred in the nucleus.)
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