catalytic core domain of RNA-dependent RNA polymerase (RdRp) in the family Barnaviridae of positive-sense single-stranded RNA [(+)ssRNA] viruses
This group contains the catalytic core domain of RdRp of RNA viruses belonging to the family Barnaviridae, order Sobelivirales, and related viruses. Barnaviridae is a family of non-enveloped, (+)ssRNA viruses. Cultivated mushrooms serve as natural hosts. The family has one genus, Barnavirus, which contains one species: Mushroom bacilliform virus (MBV) which infects the common cultivated button mushroom (Agaricus bisporus), and Bacilliform particles, which are morphologically similar to MBV, have been observed in the field mushroom Agaricus campestris. MBV viral transmission is horizontal via mycelium and possibly basidiospores. Distribution of MBV coincides with that of the commercial cultivation of Agaricus bisporus; the virus has been reported to occur in most major mushroom-growing countries. MBV is capable of autonomous replication, but commonly occurs as a double infection with a double-stranded RNA (dsRNA) virus (LaFrance isometric virus, LFIV) in mushrooms afflicted with La France disease. MBV is not required in pathogenesis involving LFIV, but it remains to be determined if it is a second, minor causal agent of LaFrance disease. MBV ssRNA and LFIV dsRNA do not share sequence homology. 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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