- Volume 26, Issue 3, 1975

The chemical and serological properties of the full, naturally occurring empty and artificially produced empty particles of foot-and-mouth disease virus, serotype A (subtype 10, strain 61) have been studied. The full 146S particles comprised the virus RNA, three polypeptides (VP1 to VP3) mol. wt. about 30 × 103, one polypeptide (VP4) mol. wt. about 13.5 × 103, and a small amount of a polypeptide (VP0) mol. wt. about 43 × 103. The naturally occurring 75S empty particles contained no RNA and much less VP1 and VP4 than were found in the full particles. However they contained a much greater proportion of VPo than the full particles. Dialysis of purified full particles against tris-EDTA, pH 7.6, produced artificial 75S empty particles which contained only a small amount of RNA and no VP4; otherwise the polypeptide composition was similar to that of the full particles. Immunological and serological tests showed that the full particles were antigenically similar to the naturally occurring empty particles but distinct from the artificial empty particles. The latter particles, however, had serological properties similar to those of the 12S protein subunit of the virus. Both the full and naturally occurring empty particles attached efficiently to susceptible cells, whereas the artificial empty particles attached only to a limited extent. The results are related to the function of the individual polypeptides of the virus particle and compared with published work on other picornaviruses.

Electrophoretic analysis of purified echovirus virus particles yielded four polypeptides of mol. wt. 37000, 30000, 25000 and 7600. The 75S empty capsids of echovirus 12 lack the 25000 and 7600 mol. wt. polypeptides, and possess polypeptides of 41000 mol. wt. A total of 14 virus-induced polypeptide species was found in the cytoplasm of infected cells. Actinomycin D reduced the synthesis of virus, virus RNA, and virus polypeptides and also reduced the proportion of virus particles to empty capsids in the virus yields.

Highly purified Sendai virus contained a protein kinase activity which catalysed the phosphorylation of endogenous polypeptides or exogenous protamine sulphate. The virus contained very low levels of phosphoprotein phosphatase activity. Polyacrylamide gel analysis of the reaction product indicated that the phosphorylation was specific for certain polypeptides and varied according to whether the virus was grown in eggs or in tissue culture. This variation was partially associated with the difference in the polypeptide pattern that occurred when the virus was grown in eggs or in tissue culture. Characterization of these phosphoproteins demonstrated that the phosphate was incorporated predominantly in a phosphoester linkage with threonine residues. Using a detergent and high salt solubilization procedure, the protein kinase activity was found associated within glycoprotein free virus particles but not with the nucleocapsid-associated polypeptides. In vivo phosphorylation occurred when Sendai virus was grown in eggs or in tissue culture with [32P] and the phosphorylated polypeptides were similar to those of the protein kinase reaction product. Phosphorylation could also be detected in the infected cell and could occur once the virus particle polypeptides were being synthesized. The non-structural polypeptides were not phosphorylated.

Fourteen strains of VEEV of diverse origin and antigenicity were classified into five virulence categories according to their efficiency of infection and nature of response in mice. Mice of ages up to 30 days represented distinct levels of responsiveness and were suitable for the differentiation of VEEV strains of highest to lowest virulence. Stepwise changes with age of the susceptibility or responsiveness of mice appeared to determine the type of response as predominantly lethal (D), dual or intermediate (DP) or protective (P).

Light and electron microscopy of spinach and Nicotiana clevelandii leaf tissue infected with parsnip yellow fleck virus (PYFV) and of chervil containing PYFV either alone or together with its ‘helper’ virus, anthriscus yellows (AYV), showed that cells of all species contained inclusion bodies not found in virus-free plants. Inclusions occurred in most types of leaf cell and consisted of vesicles probably derived from the endoplasmic reticulum, other smaller vesicular structures, and straight tubules about 30 nm in diam.; mitochondria and Golgi bodies often occurred around the periphery. Older inclusion bodies were composed almost entirely of the straight tubules.

Tubules about 45 nm in diam. and containing virus-like particles were often associated with the plasmodesmata and were sheathed by outgrowths of cell-wall material. Tubular structures occurred also in the sieve tubes and some of them contained virus-like particles. Most cell organelles appeared normal but many chloroplasts possessed peripheral vesicles bounded by a single membrane and some contained rectangular microcrystalline structures. No effects attributable to AYV were noted.

The polyamine spermidine and the diamine putrescine have been detected in coliphages T5 and ϕX174. Polyamines were identified by thin-layer chromatography and mass-spectrometry of dansyl derivatives, as well as by ion-exchange chromatography. In ϕX174 phages, polyamines were sufficient to neutralize 0.5% of DNA phosphates. The polyamine content of T5 phages depended on growth media and purification procedures, but at least 1% of DNA phosphates were neutralized by polyamines. After infection, an increase in cellular polyamine was noticed. This increase paralleled variations in ornithine decarboxylase activity.

The effect of increasing concentrations of dimethylsulphoxide (DMSO) on the stability of native and reconstituted tobacco mosaic virus (TMV) has been investigated by means of electron microscopy and infectivity assay. The removal of protein subunits from TMV by DMSO was found to be a stepwise process. Subunits are first removed from the 3′ OH end of the rod but at about 72% DMSO the site at which uncoating occurs shifts to the 5′ end. Studies with reconstituted and partially reconstituted TMV confirm the stepwise nature of the uncoating process. Complete uncoating of reconstituted TMV was found to occur at smaller DMSO concentrations than that of native TMV.

Dense poliovirus particles (buoyant density 1.44 g/ml in CsCl) isolated from infected HeLa cells contain the normal four structural polypeptides VP1 to VP4, and 35S poliovirus RNA. In addition, small amounts of VP0 and single-stranded RNA sedimenting slower than the poliovirus genome are present. Dense particles have a low specific infectivity, are neutralized by type-specific poliovirus antisera, and are detected during growth as early as normal virus but disappear when virus production stops. They appear to represent a different, more open, conformation of the normal virus capsid.

Brome mosaic virus (BMV) can be radioactively labelled by allowing virus synthesis to take place in barley leaves whose cut ends are placed in solutions of radioactive precursors of BMV. When barley plants are infected by inoculation of the first emerging leaf, the rate of incorporation of both [14C]-leucine and [32P]-orthophosphate into virus particles was found to be maximal in the second leaf, cut and labelled 4 to 5 days after inoculation. The rate of incorporation declined when the labelling or the cutting and labelling were delayed, even though assembly of particles still took place from pre-formed components. An exposure of 72 h to an appropriate amount of 32P yielded highly radioactive BMV RNA for possible sequencing studies. A specific radioactivity (32P) of the order of 1 mCi/mg RNA can be obtained readily.

Human fibroblast interferon preparations were completely stabilized to 100 °C by sodium dodecyl sulphate (SDS) in the presence of mercaptoethanol, but only a minor fraction of their activities were stabilized by SDS without mercaptoethanol. On the contrary, human leukocyte interferon preparations were completely stabilized to 100 °C by SDS in the absence of mercaptoethanol, but only a minor fraction of their activities were stabilized by SDS in the presence of mercaptoethanol.

Furthermore, human fibroblast interferon preparations whose activities had been destroyed by boiling at 100 °C were completely reactivated by SDS under reducing conditions, but only a minor part of their activities were restored by SDS in the absence of reduction. On the contrary, human leukocyte interferon preparations whose activities had been destroyed by boiling at 100 °C were completely reactivated by SDS in the absence of reduction, but only a minor part of their activities were restored by SDS under reducing conditions.

These data suggest that there are distinct molecular species of human interferons.