Detection of a Double-Stranded RNA Virus from a Strain of the Violet Root Rot Fungus Helicobasidium mompa Tanaka

Three double-stranded (ds) RNA species (ca. 1.30, 1.27 and 1.23×106) were isolated by CF-11 cellulose chromatography from a strain of the violet root rot fungus Helicobasidium mompa recovered from apple roots. Purified virion preparations contained isometric particles about 25nm in diameter, and also the same three species of dsRNA isolated from total extracts by CF-11 cellulose chromatography. The molecular mass of the coat protein was about 67K when estimated by SDS-PAGE. The largest dsRNA (referred to as dsRNA1) contains a single, long open reading frame of 1794 nucleotides that encodes a putative polypeptide containing 598 amino acid residues with a molecular mass of 69.9K. This polypeptide contains amino acid sequence motifs conserved in putative RNA-dependent RNA polymerases of RNA viruses. Phylogenetic analysis revealed similarities to RNA-dependent RNA polymerases from Atkinsonella hypoxylon 2H virus, a member of the family Partitiviridae.