catalytic core domain of RNA-dependent RNA polymerase (RdRp) in the family Narnaviridae of positive-sense single-stranded RNA [(+)ssRNA] viruses
This group contains the catalytic core domain of RdRp of RNA viruses belonging to the family Narnaviridae, order Wolframvirales. Narnaviridae is a family of (+)ssRNA viruses which are the simplest of known RNA viruses, consisting of a single molecule of (+)ssRNA that may be as small as 2.3 kb and encoding only an RdRp to direct their own replication. They encode no protein capsid and no virus particles other than lipid vesicles are known to be associated with infection. The family Narnaviridae became the second virus family with members lacking a protein capsid, following the acceptance of the family Hypoviridae as the first such family. The two genera of the family, the genus Narnavirus and the genus Mitovirus, share basic genome organization properties. The single feature distinguishing the two genera is the site of translation of the RdRp, and presumably of replication: members of the genus Narnavirus are found in the cytosol (the cytoplasm exclusive of organelles) and the genus Mitovirus are confined to mitochondria. 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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