Association of type 1 viral-like dsRNA with club-shaped particles in hypovirulent strains of Endothia parasitica

Abstract

A hypovirulent strain (H 1) of Endothia parasitica. (EP 113) contained enough dsRNA, 7 μg/g, to be detected in unconcentrated nucleic acid extracts. Two to five (the most common number) major dsRNA components (MW = 4.4–6.2 x 10 6) were detected in different preparations. A distinctive pattern of minor dsRNA components (MW < 4.0 × 10 6) was also detected. Single-stranded RNA (MW = 2.0–3.1 x 10 6) was not detected in nucleic acid samples which contained readily detectable amounts of dsRNA. Most of the dsRNA was associated with pleiomorphic club-shaped particles up to 300 nm long with spherical heads (diameter = 50–90 nm). The particles were purified from clarified extracts by polyethylene glycol precipitation and differential centrifugation. They were resolved as broad bands in rate-zonal ( S 20,W = 180 S) and equilibrium (buoyant density = 1.28 g/cm 3 in CsCl) density gradient centrifugation and had a nucleoprotein-like absorbance profile (260 nm/280 nmn ratio = 1.23–1.28) with unusual absorbance peaks at 260, 269, 280, and 293 ran. The partially purified preparation also contained large membrane-like bodies (buoyant density = 1.23 g/cm 3). Similarly prepared extracts from a virulent strain (V) lacked dsRNA, club-shaped particles, and large membrane-like bodies. All these components were also detected in extracts of a hypovirulent strain (H 2) generated by conversion of the virulent strain with strain EP 113. The appearance and properties of the club-shaped particle suggest that it is either a new and pleiomorphic type of fungal virus-like particle or a site of accumulation of a complex dsRNA.