catalytic core domain of RNA-dependent RNA polymerase (RdRp) in the family Polycipiviridae 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 Polycipiviridae (polycistronic picorna-like viruses), order Picornavirales. Polycipiviridae is a family of picorna-like viruses with non-segmented, linear, (+)ssRNA genomes of approximately 10-12 kb. Their genomes are polycistronic, with four (or more) consecutive 5'-proximal open reading frames (ORFs) encoding structural (and possibly other) proteins and a long 3' ORF encoding the replication polyprotein. Members of species within the family are typically found in ants, with Apple picorna-like virus 1 and the unnamed Polycipiviridae virus in fruit bat stool as exceptions. 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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