catalytic core domain of RNA-dependent RNA polymerase (RdRp) in the family Marnaviridae of positive-sense single-stranded RNA [(+)ssRNA] viruses, in the order Picornavirales
This group contains the catalytic core domain of RdRp of RNA viruses belonging to the family Marnaviridae, order Picornavirales. Member viruses have a (+)ssRNA genome. They are mono- or dicistronic, have a polyadenylate tail and have conserved motifs for RNA helicase, RdRp, and structural protein domains. The first RNA virus isolated and characterized that infects a marine protist was Heterosigma akashiwo RNA virus (HaRNAV) in the genus Marnavirus, that infects the toxic bloom-forming Raphidophyte alga, Heterosigma akashiwo. Recently, it has undergone a major taxonomic revision and now includes 20 species within 7 genera, which include Bacillarnavirus, Kusarnavirus, Labyrnavirus, Locarnavirus, Marnavirus, Salisharnavirus, and Sogarnavirus. RdRps catalyze RNA template-dependent formation of phosphodiester bonds between ribonucleotides in the presence of divalent metal ions. The initiation of synthesis occurs at the 3'-end of the template in a VPg-dependent manner, and proceeds in the direction of 5'-3'. The active sites of RdRps are highly conserved in different species of picornaviruses. The RdRp domain displays a right hand with three functional subdomains, called fingers, palm, and thumb. All RdRps contain conserved polymerase motifs (A-G), located in the palm (A-E motifs) and finger (F-G) subdomains. All these motifs have been implicated in RdRp fidelity such as processes of correct incorporation and reorganization of nucleotides.
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