Picornavirales

Picornavirales is an order of positive-sense single-stranded RNA viruses that infect a broad range of hosts, including humans and other vertebrates, invertebrates, and plants. Members share a common genome organization in which most species encode a single large open reading frame that is translated into a polyprotein and subsequently cleaved into structural and nonstructural proteins.

The 5' end of the genome often contains a small protein primer (VPg) rather than a typical cap, and translation commonly relies on internal ribosome entry sites (IRES). Genome sizes typically range around 7 to 9 kilobases and are usually non-segmented. The virions are generally small, non-enveloped particles with icosahedral symmetry in many members.

Replication occurs in cytoplasmic replication complexes, with the RNA-dependent RNA polymerase (3Dpol) synthesizing new genomic RNA. Viral proteases, such as 2A and 3C, mediate polyprotein processing to produce mature structural and nonstructural proteins necessary for replication and assembly.

Taxonomy and diversity: The order comprises several families, including Picornaviridae, Secoviridae, Dicistroviridae, Iflaviridae, and Marnaviridae. Picornaviridae contains major human pathogens such as polioviruses and rhinoviruses; Secoviridae includes plant-infecting viruses; Dicistroviridae and Iflaviridae include insect-associated viruses; Marnaviridae encompasses marine viruses that infect algae. The wide host range and conserved genome organization make Picornavirales a key group for studying RNA virus evolution, replication strategies, and virus–host interactions.