Use of iodinated organic compounds for the density gradient centrifugation of viruses

Proliferation of kuchijirosho causative agent in a fugu-derived cell line

Kuchijirosho is a fatal disease of commercially cultured fugu, Takifugu rubripes. The transmissible nature of kuchijirosho strongly suggests that an infectious pathogen is the causative agent. Because it is filtrable, the agent is thought to be a virus; however, it has not yet been identified. The lack of a permissive cell line for the putative kuchijirosho-causing agent (KCA) has hindered research on the identification of this pathogen. We inoculated brain extract prepared from kuchijirosho-affected fugu onto an established fugu cell line, fugu eye, and observed that cytopathic effect appeared 7 days after inoculation. Injection of the culture medium of infected fugu eye cells into fugu resulted in the onset of kuchijirosho, indicating that fugu eye cells are able to proliferate KCA. An infectious fraction separated by sodium iottalamate density gradient centrifugation showed a density of 1.15 g mL(-1) equivalent to that of KCA derived from affected fugu brain. To determine whether the genome of KCA is RNA or DNA based, nucleotide synthesis inhibitors were applied to inoculated fugu eye cell line to influence the production of KCA. 5-Fluorouracil but not IUdR showed a concentration-dependent inhibition of KCA yield. These results suggest that KCA is an RNA virus.

Lymphocytic choriomeningitis virus. IV. Electron microscopic investigation of the virion

The structure of lymphocytic choriomeningitis virus (LCM virus) was investigated by a variety of conventional as well as novel electron microscopic procedures. Thin sections of infected cells revealed the characteristic arenavirus entities whose interiors contain ribosome-like granules but look otherwise empty. In contrast, most thin-sectioned virus particles from infectious cell culture fluid, both untreated and highly purified with little loss of initial infectivity, appeared to be filled with rather homogeneous cores. Cores rather than granules were also found in positively contrasted whole and thin-sectioned virus particles. We favor the explanation that the sandy grains, which have given this group of viruses its name, are altered cores that happen to look like ribosomes. However, the alternative cannot yet be excluded, namely, that LCM virus-infected cells produce two types of particles, of which only the core-containing ones represent virions.

Purification of mengovirus by freon extraction and chromatography on protein-coated controlled pore glass

Mengovirus, extracted from infected L-cell cultures with Freon 113 and concentrated from the aqueous phase with polyethyleneglycol, was chromatographed on protein-coated controlled pore glass (CPG). The covalent binding of protein to CPG is described. Further purification and concentration of mengovirus was achieved by isopycnic density gradient centrifugation in solutions of either CsCl or salts of iodinated benzoic acid derivatives. The described procedure is superior to conventional methods for the isolation and purification of large quantities of mengovirus. It yields highly purified virus preparations within a short time and a recovery of more than 50% of the starting infectivity.

Characterization of ribonucleoproteins and ribosomes isolated from lymphocytic choriomeningitis virus

Disruption of purified lymphocytic choriomeningitis (LCM) virus with Nonidet P-40 in 0.5 M KCl followed by sucrose gradient centrifugation in 0.3 M KCl led to the isolation of two viral nucleoproteins (RNPs) as well as 40S and 60S ribosomal subunits. The largest viral RNP sedimented heterogenously at 123S to 148S and was associated with 23S and 31S viral RNA. The other viral RNP sedimented at 83S and was associated with 23S viral RNA. The buoyant density in CsCl was determined to be 1.32 g/cm3 for the viral RNP. Densities of 1.52 and 1.60 g/cm3 were determined for the 40S and 60S subunits, similar to those of the BHK-21 cells subunits dissociated by 0.5 M KCl. The viral RNPs were partly sensitive to RNase.