- Volume 23, Issue 3, 1974

The nuclei of Rous sarcoma cells were prepared from an established line of non-producer rat XC cells transformed with a Prague strain of Rous sarcoma virus (PR-RSV). Electron microscopic examination of the nuclear pellet showed a slight contamination with cytoplasmic debris and an absence of mitochondria. The DNA samples extracted from isolated nuclei and from whole XC cells were both assayed for infectivity in chicken cell cultures and found to contain about the same number of infective units per unit weight of DNA. Furthermore, the DNA from whole XC cells was set free by alkali and sedimented through an alkaline glycerol gradient in order to separate cellular DNA species according to sedimentation velocity. Under these conditions the infective RSV DNA consistently sedimented with the chromosomal 110S DNA and thus behaved as if covalently linked to the chromosomal DNA of XC cells. These results show that the infective virus DNA of non-producer RSV-transformed cells is carried in these cells as an integral part of the cellular chromosome.

Lysogens of the Mat-Ce3 mating type strain of Nocardia erythropolis were isolated from infections by nocardiophage ϕC. U.v. irradiation induced phage production in about 37% of the treated population. Phage produced from spontaneously induced populations appeared to undergo host-controlled alteration(s) which allowed it to propagate in the normally resistant Mat-cE2 mating type strains. A growth experiment performed with the infected Mat-cE2 cells showed that the phage progeny failed to inherit the capacity to propagate in Mat-cE2 strains. However, phage obtained from the Mat-Ce3 lysogens could be propagated in Mat-Ce3 hosts and still retain their ability to infect the Mat-cE2 strains. The observations may represent a new type of host-controlled phenotypic alteration of nocardiophage which acts on prophage.

Binding of the plant lectins, concanavalin A (con A), wheat germ agglutinin, soybean agglutinin and Lens culinaris agglutinin to the surface of cells infected with different Newcastle disease virus (NDV) strains inhibited virus release. Binding of succinyl-con A with a lower valency than native tetrameric con A to the surface of infected cells did not inhibit virus release. It was proposed that binding of multivalent lectin molecules to the surface of infected cells impairs assembly of the virus envelope and the budding of new virus particles by the formation of cross-linkages and lattice formation between protein molecules on the cell surface. Binding of the same lectins to NDV-infected cells also caused significant inhibition of virus-induced cell fusion. In contrast, treatment of cells with a phytohaemagglutinin preparation from Phaseolus vulgaris enhanced NDV-induced cell fusion. A new form of NDV-induced c.p.e. was observed in lectin-treated cells involving extensive damage and fragmentation of cell nuclei. This c.p.e. was also found in lectin-treated cells infected with the avirulent NDV strains F and Queensland which normally induce only limited cell damage. The possible mechanisms underlying the varied effects of different lectins on NDV release and cytopathogenicity were discussed.

Cultures of brain cells taken from mice at 1 to 3 days after peripheral infection with Chikungunya virus, showed loss of contact inhibition and morphological alterations which suggested that these cells may have been transformed. In cultures infected in vitro with a low dose of about 104 LD50/ml of culture medium, areas of epithelial-like cells and hypertrophied cells were dominant, cultures were destroyed after infection with a high dose of about 106 LD50/ml of culture medium. Cultures not destroyed by virus were studied for up to 4 months. The supernatant fluids of these cultures were titrated regularly in an adult mouse system in which the amounts of virus recorded varied from 103.7 to 106.0 LD50/ml.

Newcastle disease virus (NDV) production by individual chick embryo cells was determined after infection of monolayer cultures, trypsinization and distribution of the cells into a large number of test tubes so that each tube would contain an average of one cell (or in some experiments 10 cells). The content of each tube was assayed for p.f.u. 18 h later. The statistical analysis of the results indicates the presence of at least three distinct populations of cells with regard to NDV production: one non-producing population (50 to 90% of the cells); one low-producing population (80% of the producing cells) and one high-producing (20% of the producing cells).

The relative proportions of these cell populations was the same whether primary, secondary or tertiary cultures were used, and also when the cell-cultures were obtained from different tissues of the chick embryo.

Cells infected by FV-3 and incubated at the non-permissive temperature of 33 °C were examined by electron microscopy. In the cytoplasmic virus matrices, only irregularly shaped vesicle-like, polyhedral and tubular capsids were present. Normal particles were produced quickly by infected cells when shifted to the permissive temperature.

Dugbe virus multiplied in cell lines of pig and monkey origin producing little gross cytopathogenic effect, but prominent paranuclear, cytoplasmic inclusions were evident in stained preparations examined by light microscopy. Electron microscopic examination of thin sections of Dugbe virus-infected PS cells showed numerous virus particles 90 to 100 nm in diam. on the cell membrane and in cytoplasmic vacuoles. No virus particles were seen in inclusions, although these contained virus antigens demonstrable by immunofluorescence.

A marked prozone effect was seen in plaque titrations performed under carboxymethyl cellulose overlay. Dugbe virus-infected PS cells continued to divide and a chronically infected culture was established, which was resistant to superinfection with homologous virus. However, three togaviruses, Semliki Forest, yellow fever and Uganda S viruses, and Tahyna virus, multiplied almost as well in the Dugbe carrier culture as in control cells; Bwamba and Nairobi sheep disease viruses gave reduced yields in the Dugbe carrier cultures. It is suggested that the interference phenomenon reveals arbovirus relationships not demonstrable by conventional serological tests.

Virus-specific protein synthesis has been studied in unsynchronized and in starvation-synchronized infections of u.v.-irradiated su − host cells by ϕX174wt and a set of ϕX conditional lethal mutants. Several virus-specific protein species were detected in association with the host cell membrane at various times during the virus reproduction cycle; virus-specific proteins were also detected in the host cell cytoplasm. The intracellular distribution, between the cell membrane fraction and the cell cytoplasm fraction, of virus proteins was measured under a variety of experimental conditions. The possible significance of the presence of virus proteins on the host cell membrane is discussed.

Hybrids from poly dI and poly r(5-halogenocytidylic acids) having T m’s in the region of 60 °C are inactive as interferon inducers thus confirming the requirement for a free 2′-hydroxyl group in both the poly I and poly C strands of poly rI.poly rC.

The replication of simian virus 40 (SV40) DNA is arrested by superinfection with frog virus 3 (FV3). Most of the SV40 DNA molecules synthesized before infection by FV3 become nicked or fragmented. These events take place at 37 °C, a restrictive temperature for FV3 growth.

The compound ICI 65,709 is a substituted guanidine which has antiviral activity in human embryo lung cells (Bucknall et al., 1973). We have found that ICI 65,709 reversibly inhibits the synthesis of RNA by rhinovirus type 2. The three species of virus RNA were equally affected. Comparison of the effect with that of guanidine, a well known inhibitor of picornavirus RNA synthesis, showed that ICI 65,709 and guanidine mediated their antiviral effects in different ways. This conclusion was supported by the failure of ICI 65,709 to inhibit multiplication of a bovine enterovirus which was inhibited by guanidine. ICI 65,709 also inhibited the multiplication of poliovirus type 1.

The adenosine analogue toyocamycin which selectively abolishes the synthesis of ribosomal RNA in L cells, inhibits the antivirus activity of interferon. This inhibitory effect occurs when the cells are pre-treated with the analogue before interferon or treated simultaneously with interferon and toyocamycin. There is no inhibition of the antivirus action when the drug is added more than 1 h after the beginning of the treatment of cells with interferon.