- Volume 66, Issue 11, 1985

Hepatitis A virus (HAV) released from infected BS-C-1 cells was incompletely neutralized when incubated with a variety of convalescent sera (non-neutralizable fraction of 17 to 32%). Chloroform extraction of virus resulted in a substantial reduction of the non-neutralizable fraction (to less than 1%), suggesting that nonneutralizable virions might be associated with lipids. Non-neutralizable HAV recovered from untreated cell culture supernatant fluids sedimented heterogeneously and less rapidly than normal virus in rate-zonal sucrose gradients and also banded at a lower density in CsCl (1.14 to 1.18 g/ml) than normal, neutralizable virus (1.32 g/ml). This bimodal distribution of HAV in CsCl gradients was confirmed by cDNA-RNA hybridization. Together, these observations suggest that a substantial proportion of HAV particles released from infected cells are lipid-associated and imply an important role for cell membranes in the assembly and release of HAV in vitro.

Isometric particles of vicia cryptic virus (VCV), purified from Vicia faba seedlings infected through seed, had a buoyant density in CsCl of 1.37 g/ml. Analysis by PAGE showed that VCV particles contained three species of dsRNA with mol. wt. of 1.37 × 106, 1.26 × 106 and 1.21 × 106. These dsRNA species were also detected in extracts from leaves, stems, roots, flowers, seeds and mesophyll protoplasts of V. faba; dsRNA was readily detected in extracts from one leaflet (about 0.6 g). Slower-migrating species of dsRNA occurred in many leaf extracts but were not obtained from VCV particles. Electrophoresis of dsRNA extracts in gels that are then stained with silver appears to be a simple and reliable method for detecting ‘cryptic’ viruses. Using this method, VCV dsRNA was detected in 18 cultivars of V. faba, but not in cultivars Beryl and Minica which were thought from previous work to be free from VCV. Neither VCV particles nor VCV dsRNA were detected in VCV-free individual V. faba plants inoculated with VCV mechanically or by dodder. VCV was not detected in leaves of plants affected by cytoplasmic male sterility or in a maintainer line for this condition.