Позитивті таңғыш РНҚ вирустарының Nidovirales ордері

Order of positive sense, single stranded RNA viruses

Nidovirales is an order of enveloped, positive strand RNA viruses which infect vertebrates and invertebrates. Host organisms include mammals, birds, reptiles, amphibians, fish, arthropods, molluscs, and helminths. The order includes the families Coronaviridae, Arteriviridae, Roniviridae, Tobaniviridae, and Mesoniviridae. Member viruses have a viral envelope and a positive sense, single stranded RNA genome which is capped and polyadenylated. Nidoviruses are named for the Latin nidus, meaning nest, as all viruses in this order produce a 3' co terminal nested set of subgenomic mRNAs during infection.

Nidoviruses have a viral envelope and a positive sense, single stranded RNA genome which is capped and polyadenylated.]] The order Nidovirales can be divided into two clades depending on the size of the genome: those with large genomes (26.3–31.7 kilobases) which included the Coronaviridae and Roniviridae (the large nidoviruses) and those with small genomes (the small nidoviruses)—a clade that includes the distantly related Arteriviridae (12.7–15.7 kb). The large nidoviruses encode both a 2' O methyltransferase and a 3'–5' exoribonuclease (ExoN)—the latter being very unusual for an RNA virus. They also encode a superfamily 1 helicase, uridylate specific endonuclease (an enzyme unique to nidoviruses) and several proteases. Nidoviruses as a group have the largest RNA genomes of viruses. Group member planarian secretory cell nidovirus (PSCNV) has the largest known nonsegmented RNA genome of 41.1kb. Its host is the planarian flatworm.