- Volume 1, Issue 3, 1967

Earlier work suggested that the antiviral activity in extracts from lesions of molluscum contagiosum was due to the molluscum virus present. This has now been supported by showing a direct relationship between inhibitory activity and electron microscopically determined virus particle count in extracts from 14 patients. Using this antiviral activity as a biological marker, an analysis of the adsorption of the molluscum virus to mouse embryo cell monolayers was made. In general, the pattern of adsorption of the molluscum agent, with respect to time, temperature and inoculum volume, was similar to that already recorded in the literature for adsorption to cell cultures of the infectivity of vaccinia virus. There was a short delay between adsorption of molluscum virus and the onset of challenge virus plaque inhibition. There-after inhibition increased progressively for several hours.

In mouse embryo cells infected with polyoma virus, inhibition of DNA replication by fluorodeoxyuridine (10 µm) suppressed the production of haemagglutinin, infectious virus and viral antigen as judged by direct immunofluorescence. No virus-like particles were detected in extracts of inhibited cultures examined by electron microscopy.

The sedimentation coefficient of rubella virus was found to be 342 S and the buoyant density of 1·085 g./cm.3. The calculated particle diameter, 850 Å, was in good agreement with that found by ultrafiltration, namely 900 Å.

Human adenovirus types 1, 2, 3, 5, 6, 7, 12, 14, 16, and 21 failed to replicate beyond input titres in green monkey kidney (GMK) cells. Co-infection of the monkey cells with papovavirus SV40 stimulated replication of all the adenoviruses tested. Addition of the defective SV40 genome in the PARA particle carried by an adenovirus type 7 population enabled all the adenoviruses to replicate in the GMK cells. Growth kinetics of the adenoviruses in GMK cells co-infected with SV40 were similar to the kinetics of the virus following addition of PARA. A latent period of 16 to 24 hr was followed by an exponential increase in infectious virus between 24 and 48 hr after inoculation. Synthesis of the PARA component closely paralleled that of the adenoviruses. Both the adenoviruses and PARA remained largely cell-associated throughout the growth cycle. During the replication of the transcapsidants, the titre of the adenovirus was always greater than the titre of the PARA component. Ratios were generally in the order of 500 infectious units of adenovirus per infectious unit of PARA. These results differed from those obtained with the parent PARA-adenovirus type 7 population in which the adenovirus to PARA ratio was approximately 3:1.

DNA was extracted from purified preparations of radioactive polyoma virus labelled with either 32P or [14C]-or [3H]thymidine. Two components only (~ 20,S and ~ 16 S) were regularly isolated from all DNA preparations after velocity sedimentation. When linear gradients of increasing phosphate concentrations were applied to hydroxyapatite columns loaded with mixtures of the two components, component I (20 S) was always eluted before component II (16 S). When the two components were partially denatured under critical conditions, they were found to bind equally to the hydroxyapatite crystals; but they behaved very differently after being subjected to extensive denaturation, indicating the dependence of the chromatographic properties of the two components on their configuration.

Chromatography on hydroxyapatite was also shown to allow similarly the separation of virus and host cell DNA.

Escherichia coli strain w adsorbs phage λ very efficiently but the phage does not form plaques on this strain. In a very small fraction (10−4) of the infected cells the phage grows and produces small bursts of progeny phage also unable to form plaques on strain w. E. coli strain w is lysogenic for a temperate phage, wϕ, related to phage p2. Non-restricting hosts for phage λ became restricting hosts when made lysogenic for wϕ. When 32P-labelled λ adsorbed to restricting wϕ lysogenic hosts, > 20% of the 32P become acid-soluble shortly after infection. No wϕ specific modification was carried by the small number of λ Phages which escaped this restriction process. It is concluded that wϕ controls a host-restriction mechanism but not a host-modification process, and in parallel with other examples of host-controlled restriction and modification can be represented as r + m − or r + m°. λw mutants have been isolated which escape this restriction and which form plaques on strain w and w wϕ lysogenic strains with an efficiency of 1·. With these mutants a w-specific host modification controlled by the genome of strain w was demonstrated. Mixed infection experiments with restricted λ and unrestricted λw showed that that restricted phage did not block the growth of the unrestricted mutant nor did the mutant permit the restricted phage to grow. In addition it was shown that λ obtained from bacteria mixedly infected with λ and λw was still unable to grow in restricting hosts and λw similarly obtained from mixedly infected bacteria still retained its ability to grow on restricting hosts. It is concluded that there is a nucleotide sequence in the DNA of phage λ which, when λ infects a restricting host, is specifically recognized by the restriction mechanism controlled by the wϕ. The mutation to λw involves an alteration to this sequence such that it is no longer recognized by the restriction mechanism of the wϕ.

Mutants of wϕwere isolated not restrictive for phage λ.

Investigation of the effects of 4,5,6-trichloro-1β-d-ribofuranosyl benzimidazole and 2-mercapto-1-(β-4-pyridethyl) benzimidazole on cellular RNA synthesis and virus multiplication showed that both compounds, like actino-mycin, preferentially inhibited DNA-directed RNA synthesis. All three compounds inhibited interferon production initiated by several different viruses, and actinomycin inhibited interferon production almost as rapidly as it inhibited DNA-directed RNA synthesis. It was concluded that the compounds inhibited interferon production because of their primary action on DNA-directed RNA synthesis. Interferon production initiated by Chikungunya virus and ultraviolet-inactivated Newcastle disease virus was unaffected by addition of the inhibitors after interferon production had begun, while interferon production initiated by ultraviolet-inactivated influenza virus remained partially susceptible to the effect of the inhibitors.