Virus-like particles from killer, neutral, and sensitive strains of Saccharomyces cerevisiae

Procedures were developed for purification of virus-like particles (VLPs) from killer, neutral, and sensitive strains of Saccharomyces cerevisiae. Morphologically similar spherical VLPs measuring 40 nm in diameter were extracted from all three phenotypes. The particles were partially purified by high-speed centrifugation through a layer of CsCl (1.26 g/cm3) and sucrose density gradient centrifugation. Gradient-purified preparations contained three centrifugal species that sedimented at approximately 43, 102, and 162S. The 43S component is considered to be an artifact. Preparations from killer strains contained three double-stranded RNA (ds-RNA) components with molecular weights of 1.19 x 10(6), 1.29 x 10(6) and 2.54 x 10(6). VLPs from neutral and sensitive strains contained only the largest ds-RNA species. VLP preparations were subsequently separated into two major density components by CsCl equilibrium gradient centrifugation. The light component banding at 1.28 to 1.30 g/cm3 was void of nucleic acid, and the heavy component banding at 1.40 g/cm3 contained only the largest ds-RNA species.