RNA-dependent RNA polymerase (RdRp) in the Kobuvirus genus of positive-sense single-stranded RNA [(+)ssRNA] viruses, within the family Picornaviridae
This group contains the RdRp of RNA viruses belonging to the Kobuvirus genus within the family Picornaviridae, order Picornavirales. Kobuviruses are small, icosahedral and spherical viruses, with a (+)ssRNA genome. Unlike other picornaviruses, Kobuvirus capsids show a distinctive lumpy morphology when observed by electron microscopy; "kobu" means "knob" in Japanese. There are six species (Aichivirus A-F) in this genus. Initially, the genus Kobuvirus was divided into three species: Aichivirus A (AiVA, formerly Aichi virus), Aichivirus B (AivB, formerly Bovine kobuvirus) and Aichivirus C (AiVC, formerly Porcine kobuvirus) each possessing a single serotype. Canine kobuvirus belong to species Aichivirus A. Aichi virus infects humans, while bovine kobuvirus, porcine kobuvirus and canine kobuvirus infects cattle, swine, dogs and cats, respectively. Kobuviruses have also been detected in black goats, rabbits, European roller, and bats. RdRps are multi-domain proteins that play a pivotal role in enterovirus replication. 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 in the direction of 5'-3'. The active sites of RdRps are highly conserved in different species of kobuviruses. 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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