catalytic core domain of RNA-dependent RNA polymerase (RdRp) of the family Picobirnaviridae of positive-sense double-stranded RNA [(+)dsRNA] viruses
This group contains the catalytic core domain of RdRp of RNA viruses belonging to the family Picobirnaviridae, order Durnavirales. Picobirnaviridae is a family of viruses with bi-segmented (rarely unsegmented) double-stranded RNA (dsRNA) genomes comprising about 4.4 kbp in total, with small, non-enveloped spherical virions. The family includes one genus (Picobirnavirus) grouping three genetic clusters with high sequence variability, two defined by viruses infecting vertebrates and a third with viruses found in invertebrates. Picobirnaviruses have been identified in feces of humans, rabbits, and a variety of other species of mammals, reptiles, birds, and invertebrates. The pathogenicity of picobirnaviruses has not been established; studies conducted with immunocompromised persons suggest that they are opportunistic pathogens that may cause diarrhea. A published phylogenetic tree constructed for RdRps of RNA viruses in the realm Riboviria, showed that picobirnaviruses are embedded in the branch of diverse (+)RNA viruses; sometimes they are collectively referred to as the picornavirus supergroup. The RdRp structure of double-stranded RNA picobirnavirus is highly homologous to the RdRp of (+)ssRNA viruses. 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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