RNA-dependent RNA polymerase (RdRp) in the family Closteroviridae of positive-sense single-stranded RNA [(+)ssRNA] viruses
This group contains the RdRp of RNA viruses belonging to the family Closteroviridae, order Martellivirales. Viruses in the family Closteroviridae have a mono-, bi- or tripartite (+)ssRNA genome of 13-19 kb, and non-enveloped, filamentous particles 650-2200 nm long and 12 nm in diameter. They infect plants, mainly dicots, many of which are fruit crops. Members of the family are classified into four genera: Ampelovirus, Closterovirus, Crinivirus and Velarivirus. Their genetic diversity is primarily influenced by strong negative selection and recombination. Closteroviridae viruses are mostly phloem-restricted and induce specific cytoplasmic aggregates of virus particles intermingled with membranous vesicles derived from the endoplasmic reticulum and possibly mitochondria. Their transmission is by aphids, whiteflies, pseudococcid mealybugs or soft scale insects in a semi-persistent manner. 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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