Picornaviridae. Picornaviridae

Description of Picornaviridae adapted from ICTVdb Virion Properties Morphology Virions consist of a capsid. Virus capsid is not enveloped, round with icosahedral symmetry (T=1, pseudo T=3). The capsid is isometricand has a diameter of (22-)27-30 nm. Capsids appear round. The capsid consists of 12 capsomers. Incomplete particles are common. They are devoid of nucleic acid characterized by capsids with dark centers in negative stain preparations. Physicochemical and Physical Properties The molecular mass (Mr) of virions is 8-9 x 106. Virions have a buoyant density in CsCl of 1.33-1.45 g cm-3. The sedimentation coefficient is 140-165 S20w. Under in vitro conditions virions are relatively stable, or not stable in acid environment of pH 6. Virions are relatively stable. Virions are not sensitive to treatment with chloroform, ether, and non-ionic detergents. Nucleic Acid The genome is not segmented and contains a single molecule of linear positive-sense, single-stranded RNA. The complete genome is 7000-8500 nucleotides long. The 5'-end of the genome has a genome-linked protein (VPg). The 5'-terminus has a poly (C) tract (in some viruses, near the terminus. The 3'-terminus has a poly (A) tract. Proteins The viral genome encodes structural proteins. Virions consist of 5 structural proteins located in the capsid. Lipids LLipids are usually absent, but sometimes present in minute amounts as sphingosine-like molecules (i.e. some strains may carry 60 molecules each) and are located in the inner surface of the capsid. Polypeptide 1A (VP4) has a molecule of myristic acid covalently attached to the amino terminal glycine. Genome Organization and Replication By itself, genomic nucleic acid is infectious. Translation: The genome replicates in the cytoplasm (in complexes associated with membranes).