ENCAPSIDATION OF THE LA FRANCE DISEASE-SPECIFIC DOUBLE-STRANDED RNAS IN 36-NM ISOMETRIC VIRUS-LIKE PARTICLES

We investigated the relationship between the conserved electrophoretic pattern of nine double-stranded RNAs (dsRNAs) and the viruslike particles (VLPs) associated with La France disease of the button mushroom, Agaricus bisporus. Using a purification procedure involving chloroform extraction, PEG-NaCl precipitation, differential centrifugation, and equilibrium centrifugation in cesium-sulphate gradients, we have obtained preparations from diseased sporophores that were highly enriched in a 36-nm isometric VLP and contained minor amounts of both a 25-nm isometric VLP and the 19- X 50-nm single-stranded RNA bacilliform virus. Cesium-sulphate gradient fractions that contained these particles (average buoyant density = 1.25 g/cc) also contained the nine disease-specific dsRNAs of 3.8-0.8 kb and three disease-associated polypeptides with molecular weights of 63, 66, and 129 K. Neither the VLPs, dsRNAs, nor the polypeptides were present in healthy sporophores analyzed under identical conditions. Our data suggest that the nine dsRNAs implicated in the etiology of La France disease constitute the genome of a 36-nm isometric virus.