Purification and partial characterization of a bacilliform virus from Agaricus bisporus: a single-stranded RNA mycovirus.

A bacilliform virus from the cultivated mushroom, Agaricus bisporus, has been extensively purified and shown to be a unique mycovirus in that the genome is single-stranded (ss) RNA. The purification procedure entailed extraction at pH 6, followed by polyethylene glycol-NaCl precipitation, and differential, rate-zonal, and equilibrium centrifugation. Mushroom bacilliform virus (MBV) has a buoyant density of 1.317 g/cm(3) in Cs2SO4, A260/A280 nm absorbance ratio of 1.67, and contains approximately 20% nucleic acid by weight. SDS-polyacrylamide gel electrophoretic analyses revealed that MBV contains a single major nucleic acid species with a molecular weight of 1.4 x 108 and a single capsid polypeptide of molecular weight 24,400. The nucleic acid was hydrolyzed by pancreatic ribonuclease A in high ionic strength buffer and by 0.4 M KOH, but not by pancreatic deoxyribonuclease I. Further, the kinetics of melting of MBV RNA upon thermal denaturation closely paralleled that of the ssRNA of tobacco mosaic virus. Based on this evidence, we propose that MBV is the first mycovirus shown to possess a ssRNA genome.