- Volume 20, Issue 2, 1973

Microdrops were used to isolate interferon treated mouse L cells infected with mengovirus. Three parameters were measured, (1) the time of virus yield, (2) the yield/cell, and (3) the percentage of yielding cells. More than 97% of the control single cells yielded an average of 167 p.f.u./cell with most of them yielding between 11 and 14 h post-infection. Cells treated with interferon yielded later than controls (if at all), and all could be protected to some degree. In both treated and control cells, virus was released over a period of about 15 min. Increasing the multiplicity of infection of challenge virus reduced the effectiveness of a given interferon dose, while increasing the concentration of interferon increased the length of the latent period, decreased the size of the yield, and decreased the number of yielding cells. On the basis of these observations it is proposed that (1) the direct effect of interferon protection is to delay a critical step in virus synthesis, (2) the reduction in yield size and in the number of yielders is due to a progressive loss of the inherent ability of the cell to produce virus, and (3) the delay is the result of interferon, or a molecule induced by it, acting as a competitive inhibitor of some cellular or virus product, needed for the completion of virus synthesis.

Accumulation of intracellular mengovirus was studied in single, isolated mouse L cells. Pre-treatment with interferon delayed the initiation of virus replication in most cells, with the amount of delay varying widely from cell to cell. However, once the accumulation of intracellular virus began, it proceeded at an approximately normal rate. The data suggest that within a cell at any given moment, the action of interferon is usually all or nothing. That is, virus production is either totally inhibited, or free to proceed normally.

A count of specifically labelled tryptic peptides from purified poliovirus (strain Mahoney) showed that the amino acid sequence comprising its structural protein contains at least 21 and 25 uniquely placed residues of histidine and methionine, respectively. Amino acid analysis after performic acid oxidation showed a content of, respectively, 21 and 27 moles of these residues per 1000 amino acids recovered. Accordingly, poliovirus structural protein must comprise a unique sequence of about 1000 amino acids, representing about 40% of the coding potential of the poliovirus genome. The correspondence of this percentage with the proportion of the poliovirus genetic map occupied by structural protein genes (48%) suggests that the map represents a major part of the genome. A value of about 1000 amino acids, or 100 to 110000 daltons of protein, for the repeating structural unit, coupled with a total content of 6.0 to 6.4 × 106 daltons of protein in the poliovirus particle, indicates that it contains 60 such structural units and that its triangulation number = 1.

A mutant of the virus of foot-and-mouth disease (O type) was studied, and shown by electrophoresis in SDS-polyacrylamide gels to contain equimolar proportions of four polypeptides with mol. wts. of 34, 20, 17 and 14 × 103. Two minor components were also present with mol. wts. of 51 and 25 × 103 and in the molar ratio of 0.07 and 0.28. Only the polypeptide of mol. wt. 34 × 103 was labelled when the intact virus was iodinated. This polypeptide was sensitive to the action of trypsin and showed leucine as the N-terminal amino acid. Our own and other results are discussed in terms of virus structure.

Feline leukaemia viruses of subgroups B and C multiply in human and canine cells, while subgroup A viruses do not. This host range restriction is determined by the virus envelope and operates at the level of virus entry into the cell. Subgroup A virus genomes are expressed and replicated when they are introduced within B subgroup envelopes into human or dog cells. Therefore, since they are phenotypic mixtures of A and B subgroup viruses, the majority of feline leukaemia virus isolates will infect human and canine cells with the subsequent production of FeLV of each subgroup.

Tobacco protoplasts were infected with cowpea chlorotic mottle virus and its RNA in the presence of poly-l-ornithine to yield 106 to 107 particles per infected protoplast representing a probable increase in virus concentration of at least 1000-fold by 24 to 72 h after inoculation. The optimum inoculum input for virus was about 0.5 µg/ml and for RNA about 1.2 µg/ml; about 60 and 7%, respectively, of the protoplasts became infected, as judged by fluorescent antibody staining. Data relating to growth curves, inoculum and poly-l-ornithine concentrations, and pH effects are presented along with electron micrographs of sectioned protoplasts.

Six polypeptides could be detected in purified preparations of adenovirus type 12 by polyacrylamide gel electrophoresis. One of these polypeptides (the Y polypeptide) could not be seen in type 5 virus preparations and appeared to be associated with the core components rather than with the capsid components. Incomplete particles of type 12 virus, while lacking the core polypeptides contained three other polypeptides. The synthesis of the structural polypeptides could be detected in infected cells by labelling with [35S]-methionine; in addition, there were at least eight other polypeptides which appeared to be specific for the infected cell (ICSP’s). One of these, ICSP-3, of mol. wt. 55000, was synthesized early in infection even in the presence of an inhibitor of DNA synthesis and was thus presumed to be related to the adenovirus type 12 tumour (T) antigen. Phosphorylation of polypeptides was noted in the infected cells and in the purified virus both fibre and core-1 polypeptides appeared to be phosphorylated.

Representative myxoviruses were inactivated by cultures of normal human or mouse lymphoid cells even after stimulation with a variety of mitogens. The fractionation of cells by velocity sedimentation indicated that inactivation occurred in the presence of some lymphocyte populations but not macrophages. Pretreatment with neuraminidase prevented this effect. Cells producing antibody to sheep RBC failed either to adsorb or to inactivate virus. The direct inactivation of myxoviruses by normal lymphoid cells may be one of the mechanisms involved in host resistance against viruses of this group.

In cultured Aedes albopictus cells at 28 °C, Semliki Forest virus (SFV, an alphavirus; Wildy, 1971) shows a latent period, growth rate and yield per cell similar to that obtained with the same virus in three vertebrate cell lines at 37 °C. SFV and the flavivirus Kunjin both grow more slowly and to lower titre in A. aegypti cells (Peleg, 1968) than in A. albopictus cells. Kunjin grows more slowly than SFV in both mosquito and vertebrate cell lines. No replication of either virus occurred in another A. aegypti cell line (Grace, 1966).

The effect of adsorption conditions on the percentage of Aedes albopictus cells infected by SFV is examined. In both mosquito and Vero cells the temperature giving the shortest latent period of SFV growth is close to the optimal temperature for cell growth. No c.p.e. were visible in infected mosquito cells; this contrasts with the invariant destruction of vertebrate cells.

DNA-R, a replicate intermediate of adenovirus type 2 (ad. 2) DNA with a linear structure, contains a small amount of single-stranded material which can be digested by specific nucleases. The sedimentation properties of the digestion products are consistent with the assumption that DNA-R represents molecules of ad. 2 DNA replicating unidirectionally.

A murine leukaemia virus helper-independent strain of Moloney sarcoma virus (MSV), designated S + L -, was isolated from cells transformed by MSV in the absence of replicating leukaemia virus. The virus is non-infectious in tissue culture as evidenced by its failure to replicate in a variety of murine cell lines.

Sucrose gradient and gel electrophoretic analyses of the purified S + L - isolate showed that the virus contains 60 to 70 S RNA. The virus also possesses RNA-dependent DNA polymerase (RDDP) activity.

On the basis of these data it would appear that factors other than high mol. wt. RNA and RDDP may account for the lack of infectivity of this strain of MSV.

Mouse mammary tumour virus contains an RNA-dependent DNA polymerase. The enzyme requirements and physical properties of the reaction products are similar to those of other RNA tumour viruses, despite the unique characteristics of the virus in other properties.

The length of the Pseudomonas aeruginosa filamentous bacteriophage Pf was found to be 1915 ± 77 nm, as measured in the electron microscope using the Kleinschmidt spreading technique. Pf is thus the longest filamentous phage so far isolated. Coliphage If, the I-specific filamentous phage, is nearest to it with a length of 1300 nm.

Hepatitis B (Australia) antigen was isolated from normal serum proteins by gel filtration and electrofocusing. The latter technique revealed a heterogeneity of the small spherical particles associated with hepatitis B antigen activity, there being a variance in determined isoelectric points according to the serological subtype studied. Hepatitis Bantigen isolated in this manner was aggregated by concanavalin A.

This paper presents the results obtained from a comparative study of some growth and antigenic properties of four subclones of hamster cells transformed by SR-RSV. A positive correlation was found between the growth potential of the cells in soft agarose containing dextran sulphate, and the degree to which they expressed the surface antigen (VISA) induced by the Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV).

The infectivity and the haemagglutinin activity of A2/Aichi/2/68 influenza virus were unchanged during a 2-year storage in allantoic fluid at -80 °C. Over the temperature range from -20 to + 37 °C, exponential slopes could be drawn by means of the regression analysis, the velocity constants showing very low values. Conversely, at + 56 °C inactivation took place in a two-component fashion, each following first-order kinetics. Haemagglutinin and neuraminidase activities were not impaired by exposure to [60Co]-γ-rays (3 × 106 rad), which completely removed infectious particles. The specific rate constants for inactivation of haemagglutinin and neuraminidase activities of untreated and irradiated virus were overlapping when samples were stored for 2 years in the frozen state (- 80 and - 20 °C), whereas a significantly increasing rate of inactivation was recorded for γ-irradiated samples following storage at temperature above 4 °C. Nevertheless, the energy of activation required for thermal inactivation was very low and the entropy of activation showed negative values for both the untreated and the irradiated virus preparations.