Positive-strand RNA virus
Positive-strand RNA viruses (+ssRNA viruses) are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated into viral proteins by the host cell's ribosomes. Positive-strand RNA viruses encode an RNA-dependent RNA polymerase (RdRp) which is used during replication of the genome to synthesize a negative-sense antigenome that is then used as a template to create a new positive-sense viral genome.
Positive-strand RNA viruses are divided between the phyla Kitrinoviricota, Lenarviricota, and Pisuviricota (specifically classes Pisoniviricetes and Stelpavirictes) all of which are in the kingdom Orthornavirae and realm Riboviria.[1] They are monophyletic and descended from a common RNA virus ancestor. In the Baltimore classification system, +ssRNA viruses belong to Group IV.[2]
Positive-sense RNA viruses include pathogens such as the Hepatitis C virus, West Nile virus, dengue virus, and the MERS, SARS, and SARS-CoV-2 coronaviruses,[3] as well as less clinically serious pathogens such as the coronaviruses and rhinoviruses that cause the common cold.[4][5][6]
Genome[edit]
Positive-strand RNA virus genomes usually contain relatively few genes, usually between three and ten, including an RNA-dependent RNA polymerase.[4] Coronaviruses have the largest known RNA genomes, between 27 and 32 kilobases in length, and likely possess replication proofreading mechanisms in the form of an exoribonuclease within nonstructural protein nsp14.[7]