Particle properties of parsnip yellow fleck virus

Particle preparations of parsnip yellow fleck virus (PYFV) isolates A-421 and P-121, representing the two major serotypes, were made by clarifying leal extracts with ether or butan-1-ol and concentrating the virus particles by precipitation with polyethylene glycol and differential centrifugation. The preparations contained c. 31 nm-diameter particles comprising two sedimenting components. Top component (T) consisted of stain-penetrable protein shells with A₂₆₀/A₂₈₀= 0.8–0.9, sedimentation coefficient (S₂₀) = 56 S (A-421) or 60 S (P-121), and buoyant density = 1.297 g/cm³. Bottom component (B) consisted of nucleoprotein particles, not penetrable by negative stain, with A₂₆₀/A₂₈₀= 1.9, sedimentation coefficient (S⁰_20.w) = 148 S (A-421) or 153 S (P-121), and buoyant density = 1.520 g/cm³ (A-421) or 1.490 g/cm³ (P-121). Yields of B component particles were up to c. 1 mg/100 g leaf tissue (both isolates); yields of T component particles were up to c. 0.6 mg (A-421) or 5.5 mg (P-121) per 100 g leaf tissue. PYFV particles were found to contain a single RNA species (mol. wt c. 3.4 × 10⁶, c. 9800 nucleotides), constituting 40% of the particle weight, and three polypeptide species, of mol. wt (× 10 ³) 30 , 26 and 24 (A-421) or 31 , 26 and 23 (P-121).