Order - Picornavirales

Abstract

This chapter focuses on the Picornavirales order, which contain viruses with a monopartitite or bipartite positive-strand RNA genome. Members of the family Picornaviridae (genus Enterovirus) and of the family Secoviridae (genus Comovirus) were the first characterized members of the order, which infect vertebrates and plants, respectively. The order also includes viruses infecting invertebrates (families Dicistroviridae and Iflaviridae) or algae (family Marnaviridae). The virions are nonenveloped icosahedral particles approximately 30 nm in diameter with a pseudo- T = 3 symmetry and their preparations often contain empty virus particles. Most members of the order have a single molecule of positive sense RNA ranging between 7,000 and 12,500 nt in length. Some members of the order (genera Comovirus, Fabavirus, Nepovirus, Sadwavirus, Cheravirus, and Torradovirus all in the family Secoviridae) have a bipartite genome with an RNA1 ranging in size between 5800 and 8400 nt, and an RNA2 between 3200 and 7300 nts. Their capsid contains 60 units, each consisting of three paralogous jelly-roll domains, where each jelly-roll domain is unique in sequence but folds in a similar 8-stranded beta-barrel structure. In most members of the order, the three jelly-roll domains are contained in three separate coat proteins (CP) of approximately 25 kDa each. The viral RNA is infectious and serves as a template for replication and as mRNA. In the case of viruses with a bipartite genome, RNA1 can replicate independently of RNA2 within the first infected cell but RNA2 is required for encapsidation and for cell-to-cell movement. Members of the order infect a wide range of hosts including vertebrates (family Picornaviridae), plants (family Secoviridae), arthropods (family Dicistroviridae and Iflaviridae), and unicellular organisms (family Marnaviridae).