VESICLE-ASSOCIATED DOUBLE-STRANDED RIBONUCLEIC-ACID GENETIC ELEMENTS IN AGARICUS-BISPORUS

Double-stranded ribonucleic acids (dsRNAs) were isolated from fruit bo dies of commercial strains of the cultivated mushroom (Agaricus bispor us) by polyethylene glycol-NaCl precipitation, differential centrifuga tion, rate-zonal centrifugation in sucrose, and equilibrium centrifuga tion in cesium sulphate. In all seven of the mushroom isolates examine d, three dsRNAs were identified: two major dsRNA segments of > 13.1-kb (L-RNA) and 2.4-kb (S-RNA) and a minor segment of 5.2-kb (M-RNA). L-, M-, and S-RNAs co-purified with spherical fungal vesicles measuring a pproximately 75 nm in diameter. The three dsRNAs were intimately assoc iated with the vesicles as suggested by their lower buoyant density in cesium sulphate (1.27 g/cc) compared to that of phenol-extracted dsRN As (1.42 g/cc) and by their resistance to hydrolysis by ribonuclease a t low ionic strength. Using a variety of conditions during purificatio n, no virus-like particles were found to be associated with the dsRNAs . In Northern analysis, L-, M-, and S-RNAs failed to cross-hybridize w ith the genomic dsRNAs of La France isometric virus. We report here th e first description of non-encapsidated, vesicle-associated, dsRNA gen etic elements in the common cultivated mushroom.