- Volume 22, Issue 1, 1974

The effect of interferon on interferon induction either by NDV or poly I:C was studied. A priming effect of NDV-induced interferon was obtained after pretreatment of the cells for 24 h with low concentrations of homologous interferon. After pre-treatment with higher doses, interferon production was diminished. Purified homologous interferon preparations had a biological effect similar to that of unpurified preparations, while purified heterologous interferon had no effect. The destruction of the interferon molecule or of ‘associated proteins’ by trypsin abolished the blocking effect. Similar results were obtained when poly I:C was used, instead of NDV, as an inducer. In somatic monkey-mouse hybrid cells, mouse or monkey interferon was effective in blocking mouse or monkey interferon synthesis. In clones weakly sensitive to primate interferon, no significant effect was observed.

The structural proteins of vesicular stomatitis virus (VSV) Indiana, VSV New Jersey, Chandipura virus and Piry virus were compared by using two different SDS-polyacrylamide gel electrophoresis systems. The G and M proteins of the Indiana serotype had different electrophoretic mobilities from the corresponding proteins of VSV New Jersey, Chandipura virus and Piry virus in a continuous-SDS (CONT-SDS) gel system. The three major proteins of VSV Indiana G, N and M, were distinctly different from their counterpart proteins in the other three viruses when a high-resolution discontinuous-SDS (DISC-SDS) system was used. Chandipura and Piry virus glycoproteins migrated differently when co-electrophoresed in the CONT-SDS system, whereas both their N and M proteins were different in the DISC-SDS method. During infection both Chandipura and Piry viruses produced defective T particles which contained the same four structural proteins as virus particles.

The neuraminidase of the Rostock strain of fowl plague virus (FPV) was found to be serologically closely related to the enzyme of swine influenza virus, whereas the haemagglutinins were distinct. When chickens were immunized with the apathogenic swine influenza virus, they were fully protected against an infection with the highly pathogenic FPV which killed non-immunized birds within 2 days. These experiments provide conclusive evidence that a protective capacity can also be attributed to the neuraminidase of influenza viruses.

The influence of hydrogen bonding on the structure of tobacco mosaic virus (TMV) was studied by reacting dimethylsulphoxide (DMSO) with two strains of the virus (Wild-type and G-TAMV) which differ in coat-protein amino acid composition.

Reaction mixtures were spread by the Kleinschmidt technique and the samples studied in the electron microscope.

The complete particles of the two strains showed a difference in stability. Wild-type needed 74% but G-TAMV only 55% DSMO. Fragmented particles present in the original samples were uncoated by DMSO at a lower concentration than complete particles, suggesting that the ends of complete particles are particularly strongly bonded. With increasing concentrations of DMSO, G-TAMV was uncoated stepwise suggesting strong bonding between RNA and protein at certain places on the RNA.

With high enough concentrations of DMSO all particles were completely stripped leaving only RNA. The infectivity of the preparations was then the same as that of phenol-extracted RNA. The infectivity of partially stripped rods was greater than that of the completely stripped RNA but less than that of complete rods.

Regardless of the input multiplicity used in propagating simian virus 40 in monkey kidney cells, virus populations essentially devoid of defective viruses still contain three types of particles: heavy virus (ρ = 1.35 g/ml), light virus (ρ = 1.325 g/ml) and ‘empty’ capsids (ρ = 1.30 g/ml). Neither light nor heavy virus fractions contain lipids. The protein moiety of the three particle forms is composed of the same polypeptides in similar proportions. DNA extracted from the light virus fraction sediments at a rate identical to that of DNA from heavy virus both in neutral and alkaline sucrose density gradients. The two DNAs hybridize with the same efficiency with the DNA from heavy virus and band together after isopycnic centrifuging in CsCl solution containing ethidium bromide, indicating structural similarity. The sedimentation rates of heavy and light virus particles and their sizes as determined by electron microscopy, are also similar. However, the protein to DNA ratio in the light virus fraction is twice that in the heavy virus fraction. Thus, either heavy virus particles contain two double-stranded, circular DNA molecules of identical molecular size, and light particles contain one, or the light virus fraction contains aggregates of heavy virus and particles devoid of DNA in equal proportion. The specific infectivity of heavy virus is about ten times larger than that of light virus, but the specific infectivity of virus DNA isolated from these virus forms is similar.

A study was made of the mechanism of microfocus formation and of the nature of the inclusion bodies that appear in the cytoplasm of RK-13 cells infected by rubella virus.

Direct passage of virus particles from one cell to another, at least in the early stages of the infection, is posed as a possibility, and the lysosomal nature of the cytoplasmic inclusion bodies is demonstrated by histochemical methods. A description is given of conditions required in the monolayer for the formation of a microfocus, which is the characteristic manifestation of the c.p.e. of the rubella virus in this cellular system.

The RNA content of four different CMV strains was investigated. All RNA preparations always contained the four major RNA species described by Kaper & West (1972), while most preparations also contained several minor RNA species. The four largest RNAs were separated by sucrose density-gradient centrifuging and by electrophoresis on polyacrylamide gels. Combination experiments suggest, for all strains, that the genome consists of the three largest RNAs (1 + 2 + 3), while RNA 4 is not required for infectivity.

The distribution of RNAs in the capsids could not be established unequivocally, and the situation possibly differs in different strains.

Some activity (1 to 10%) was recovered from partially purified leukocyte interferon which had been reduced by mercaptoethanol and allowed to oxidize in air. The recovery was complete if the reduced interferon was unfolded by guanidine hydrochloride or urea. Oxidation in the continued presence of these denaturants lead to incomplete recovery (3%). Carboxymethylation of reduced interferon permanently destroyed all activity. Sodium dodecyl sulphate did not cause any loss of interferon activity but did hinder successful re-oxidation in the presence of urea. The prime importance of at least one disulphide bond in interferon structure is indicated. Further confirmation was obtained by oxidative cleavage of disulphide bonds. The lack of effect of p-chloro-mercuribenzoate suggests that free thiol groups are not important for antiviral action.

The proteins of the virus particles, empty capsids, and 12S subunits of foot-and-mouth disease virus were compared by polyacrylamide gel electrophoresis in neutral phosphate buffer with SDS and in 1 m-propionic acid with urea. In the first system the mol. wt. of the observed components were estimated and in the second system proteins with similar mol. wt. were resolved by their different charges. The proteins were either denatured by urea, reduced by mercaptoethanol, or oxidized by performic acid. They were dissociated completely only by reduction or oxidation. By denaturation with 8 m-urea, dimers with mol. wt. of about 58000 were observed. In propionic acid-urea electrophoresis, each of the three virus types A2 Spain, O1 Kaufbeuren and C Upper Bavaria showed three main proteins (VP 1, VP 2, VP 3) and a fourth fast-migrating protein, VP4. The rates of migration of VP 1 and VP 3 were approx. the same in all types, whereas VP 2 showed differences between types. The component VP 4 was not present in the empty capsids or in the 12 S subunits. On elution of the proteins from the gels used in propionic acid-urea electrophoresis followed by re-electrophoresis in both systems, it was found that the relative electrophoretic migration rates of VP 1 and VP 3 were opposed in the two systems. The oxidized proteins VP 1, VP 2, and VP 3 had similar mol. wt. of about 26000 to 28000 but varied in charge. Of the native virus, only one protein was split by trypsin, leaving two detectable fragments of 9500 and 18500 daltons.

The requirement of arginine for the replication of Marek’s disease herpes virus (MDHV) was studied in Japanese quail embryo fibroblast cell (QEFC) cultures. Arginine was essential for the replication of MDHV in QEFC cultures. The plaqueforming activity of MDHV was inhibited by omission of arginine from the medium but resumed upon addition of arginine in arginine-deprived infections. The MDHV genome survived in a recoverable form in infected cultures kept in arginine-deprived medium for up to 10 days. Arginine was required around or after 12 h following inoculation. Omission of arginine from the culture medium did not affect virus adsorption, penetration, or the synthesis of virus DNA but did prevent the formation of virus structural protein which was detectable using immunofluorescent antibody techniques.

When incubated in vitro at 40 °C, chorioallantoic membranes produce 80 to 200 p.f.u./cell of Newcastle disease virus (NDV), whereas chick embryo cells and mouse L cells produce only 2 to 10 and 0.1 p.f.u./cell, respectively. Under such conditions NDV ‘minus’ strand RNA accumulates in chick embryo cells (as well as in mouse L cells) but not in chorioallantoic membranes.

Lowering the incubation temperature from 40 to 36 °C resulted in delays in virus release by 5 h from chick embryo cells, but by 1 h from chorioallantoic membranes. The maximum rate of virus RNA synthesis was observed at times when the release of progeny virus had been terminated.

When protein synthesis is inhibited by early addition of cycloheximide, some NDV ‘minus’ strand RNA is found in the chick embryo cells but not in the chorioallantoic membranes. When the inhibitor is added later (2 h after virus infection), no virus RNA is labelled in the chick embryo cells, although some ‘plus’ strand RNAs are found labelled in the chorioallantoic membranes.

It is suggested that the observed difference in the permissiveness of various cell types for NDV depends on the amount of some cellular component involved in NDV ‘plus’ strand RNA synthesis.

The infectious agent in culture fluids of serially passed nuclear polyhedrosis virus of the cabbage looper (Trichoplusia ni) sediments at 830S. Infectivity falls below detectable limits when virus concentrates are treated with either deoxycholate (DOC) or with Tween-ether, and the sedimentation coefficient becomes 325S. The buoyant density in CsCl of several virus preparations was in the range 1.26 to 1.35 g/ml and increased to 1.42 in all cases after DOC treatment. The results indicate that the non-occluded form of the virus produced in tissue culture consists of fragile enveloped particles.

A particle about one third of the length of the virus particle and containing single-stranded RNA has been found in BHK cells infected with rabies virus. The particle interferes with replication of rabies virus and contains RNA which sediments at 20S compared with 43S for virus RNA.

The characteristics of 4 closely related bacteriophages of halotolerant, collagenolytic strains of Achromobacter isolated from cured hides are described. All phages cause lysogenic conversion. Achromobacter sp. 2 is shown to be a cryptic lysogen for phage α3 and has a low rate of spontaneous liberation which can be increased by treatment with mutagens. An explanation for the cryptic lysogeny is proposed.