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The growth of vaccinia virus in monolayers of BSC-1 cells enucleated by centrifugation in the presence of cytochalasin B has been studied. No evidence for the production of infectious virus in these cells was obtained, and the production of virus particles was reduced to 8.3% compared with the yield from cytochalasin-treated, uncentrifuged cells. Virus DNA and early and late polypeptides were synthesized with normal timing in enucleate cells, but in reduced amounts; cleavage of structural polypeptide precursors P4a and Px also occurred in enucleate cells. Factories containing immature virus particles were demonstrated in enucleate cells by electron microscopy; these factories were reduced in number and size compared with those found in cytochalasin-treated, uncentrifuged cells.

The requirement of the presence of a nucleus for the replication of vesicular stomatitis virus and influenza virus has been examined by following the growth and development of these viruses in enucleate BS-C-1 cells. Vesicular stomatitis virus replicates normally in enucleate cells with the rate of production of infectious virus, the amount of virus-specific protein synthesis, and the type of proteins produced being essentially the same in nucleate and enucleate cells. Influenza virus does not replicate in enucleate cells, no virus gene products can be detected, and there is no inhibition of cellular protein synthesis.

The mineralogy of the clay fractions of two soil profiles representing the end-members of a catena developed on a glacial till derived from basic lavas has been determined. Particular attention has been given to the assessment of the nature of the amorphous inorganic material in the clay fraction of these soils. Chemical dissolution techniques were used and their effects on the clay fraction were followed by X-ray diffraction, differential thermal, infrared absorption, electron-optical and surface area measurements. The principal conclusion is that the soil clays are a continuum from completely disordered, through poorly ordered to well crystallized material.

The removal of the alkali-soluble fraction from soil clays has been found to influence markedly the efficiency with which iron oxides can be removed from such clays. In clays pretreated with 5% Na2CO3, up to 40% more iron oxide was extracted by dithionite (Na2S2O4) than from soil clays treated with this reagent alone. Chemical analysis, electron microscopy, X-ray and differential thermal examination, and specific surface area and cation-exchange capacity measurements indicated an improved dispersion brought about by the removal of aluminosilicate binding material by Na2CO3. The electron-optical studies also showed that the dithionite-soluble iron was principally in the form of small granules. These were amorphous to X-rays and electrons and chemical analysis of the dithionite-soluble fraction suggested that they were ferruginous complexes containing considerable quantities of silica and alumina.

Ultra-thin sections of a synthetic graphite have been examined in the electron microscope before and after oxidation in air at a temperature of 500 °C. In unirradiated material, micrographs of individual areas showed that oxidative attack occurred at grain boundaries and at pores between individual crystallites. Parallel experiments on material which had been irradiated to a dose of 8.7 x 10 19 n .v .t. again showed etching at pores and at grain boundaries, but, in addition, in the majority of specimens, a shallow surface pitting of the entire (0001) faces of the individual crystallites took place. The density of these shallow pits varied from 5 x 10 10 /cm 2 to 5 x 10 u /cm 2 . Variations in reaction rate were observed and were traced to impurity which, especially when metallic, greatly increased the oxidation rate. In unirradiated graphite, this impurity appeared to be absorbed only at pores and intercrystallite boundaries, oxidation effects being observed only at these sites. In irradiated material impurity was also absorbed at sites on the (0001) crystal faces where oxidation produced etch pits of widely varying depth and density. Channelling of the (0001) layer nets occurred in both irradiated and unirradiated specimens. Annealing of the irradiated graphite at 650 °C for 1 h produced no significant change in the pattern of attack by oxygen. The observed etch pit density measured on the (0001) layer nets was 8 x 10 10 cm 2 . A mechanism for pit formation relating pit density and vacancy content is proposed. The general appearance of irradiated samples differed from the unirradiated in that the well-defined moire patterns characteristic of thin sections of synthetic graphite were absent in irradiated samples, but reappeared when the samples were annealed at 650 °C. This change is related to the known behaviour of interstitial atoms in graphite on annealing the materials

Summary Examination of the physical structure of cauliflower mosaic virus DNA by electron microscopy and ultracentrifugal analysis showed that the DNA could be isolated mainly as a circular molecule of mol. wt. 4.7 × 106. Nearest-neighbour frequency analysis showed that the DNA has a chemical structure which exhibits close similarities to that of the host cauliflower DNA. The relationships of this plant virus DNA and the small mammalian virus DNAs to the DNA of their respective hosts are discussed.

The ultra-microtome has been used to obtain thin sections of synthetic graphite blocks. The thickness of the sections was measured by shadowcasting and measuring the shadow length at appropriate edges. An average value of 150 Å was obtained. Transmission electron micrographs of thin sections showed moire patterns and the interrelation of these moire patterns revealed a characteristic grain structure in graphite akin to that seen in metals but with component microcrystals of smaller dimensions. The area of the individual micro - crystals forming the grain structure was measured and was found to be 0·11 + 0·074μ 2 . The boundary between neighbouring microcrystals was narrow and of around 50 A in width. Pores were visible at the junction of three or more contiguous microcrystals and were of diameter 400 to 800 Å. The selected-area electron diffraction technique was used to determine the orientation of individual microcrystals in the graphite sections. It was found that the hexagonal layer net planes were lying parallel or at a very small angle to the plane of the section. The electron diffraction patterns were also used to correlate the layer stacking faults in individual microcrystals both by counts of individual reflexions on the (1120) diffraction ring and by counts of the extra reflexions due to the long spacings between successive displaced layers. The average value of 13 Å found for the distance between successive stacking faults is equivalent to the distance between four hexagonal layer net planes. The moire patterns in the electron micrographs could be related to the long spacings in the electron diffraction patterns. It was possible to calculate the angle of twist between successive stacking faults from the long spacing or from the moire pattern. Dislocations were seen in many of the thin sections and were observed as extra terminating half-lines in the moire patterns; these dislocations were present in the hexagonal layer net planes themselves and indicated that there was in this region a considerable deformation of the benzenoid structure of the hexagonal layer nets. The measured frequency for their occurrence was 3·3 x 10 7 /cm 2 . Slip planes were also detected in some specimens.

The relationship between culture density and the number of microvilli on the cell surface has been studied using BHK21 cells in established monolayer culture. The number of microvilli can be estimated quantitatively by a scanning electron-microscope technique. It can be increased by applying specific antiserum, but whether antibody is applied or not a significant number of cells regularly bear microvilli. This number is characteristic of the culture density. In sparse cultures above a certain minimum density it is relatively high, and in confluent cultures it is much reduced. These results indicate that microvilli may be inhibited by cell contact.

The effect of a number of rifamycin derivatives and related compounds on the reversibility of the rifampin-induced virus maturation block was studied by using BHK-21 cells infected with vaccinia virus. All of the derivatives of 3-formyl rifamycin SV maintained this block, the required concentration varying from 100 to 1,000 μg/ml. These compounds vary only in the nature of the side-chain attached to the 3C atom on the naphthohydroquinone moiety; no obvious correlation between the nature of this side-chain and antiviral activity was found. Streptovaricin complex and tolypomycin R also maintained the maturation block; tolypomycin also produced marked alterations in the appearance of the viroplasm contained in rifampin-induced inclusions and immature virus particles.

Summary Infectivity titration, sedimentation analysis in sucrose gradients and electron microscopy have been used to study virus maturation following the reversal of the inhibition of vaccinia virus growth by rifampicin. Electron-dense inclusions containing tubular structures develop in the cytoplasm of infected BHK 21/C 13 cells maintained in rifampicin, but the formation of immature and mature virus particles is prevented. The removal of rifampicin is followed by a rise of the virus infectivity. Spicule-covered membranes appear at the periphery of the inclusions and both immature and mature virus particles are seen. A proportion of the DNA synthesized in the presence of rifampicin is incorporated into particles and becomes resistant to deoxyribonuclease I. If protein synthesis is inhibited, spicule-covered membranes and immature particles appear but no mature particles are seen; the virus infectivity does not increase and the DNA remains susceptible to deoxyribonuclease I. It is suggested that rifampicin binds reversibly to a virus-specified protein, thereby preventing the formation of immature virus particles. Possible effects of rifampicin on the subsequent stages of virus maturation are discussed.

THE antibiotic rifampicin inhibits the growth of bacteria by inhibiting DNA dependent RNA polymerase1,2. It also inhibits the growth of vaccinia and other poxviruses3,4. An interaction between the antibiotic and the viral polymerase has not been demonstrated, however, and the antiviral mode of action of the drug remains unknown.

Summary Rabbit kidney vacuolating virus is similar to polyoma virus in the size and structure of the virus particle. The DNA of the virus is also similar to the DNA of polyoma virus, being supercoiled and circular with a molecular weight of approximately 3 million. The base composition of the DNA, 43% guanine plus cytosine (GC), is intermediate between that of polyoma virus DNA, 48% GC, and that of simian virus 40 DNA, 41% GC. It is concluded that rabbit kidney vacuolating virus should be placed with polyoma virus and simian virus 40 as a member of the polyoma group of viruses.

The cell surface of a non-fruiting myxobacterium,Cytophaga johnsonii, was investigated by electron optical techniques. Negative staining revealed an irregularly undulating surface topography and the presence of strands of material arising from the cells. Replicas of freeze-dried cells and thin sections confirmed the uneven nature of the surface and showed that, in contrast to eubacteria, the cell was surrounded by an envelope of amorphous, electron-translucent material contained within a crenated, outer, “unit” membrane. This material could be extruded as long strands. It is considered that this envelope of material represents the slime layer of the organism. The appearance of the slime layer at various stages in the growth of the organism was followed by negative staining and the image of the organism presented by negative staining was compared to that given byMyxococcus xanthus andFlavobacterium aquatile.

SUMMARY: Electron microscopic study of vibrio flagella by using the negative staining technique revealed differences in chemical reactivity as between the sheath and core components. The sheath was easily degraded by autolysis and exposure to acid and urea, whereas the core was relatively resistant. These differences suggest that the sheath and core are of different composition and that, whereas the core consists of the protein ‘flagellin’, the sheath is probably of cell-wall origin.

Summary The nearest neighbour frequency pattern analyses of the DNAs of a minute virus of mice, Kilham rat virus and H-1 virus were very similar to each other. They were also similar to the pattern of the host cell DNA, apart from differences related to structure, the virus DNAs being single-stranded and the host double-stranded. All three DNAs exhibited the low frequency of the dinucleotide sequence CpG previously found in mammalian DNAs and in the nucleic acids of small mammalian viruses. The sizes and densities of the virus particles were measured, and the molecular weight of H-1 DNA was determined.

Summary The base composition of DNA from a minute virus of mice was determined by hydrolysis of 32P-labelled DNA to give 3′ and 5′ nucleotides. The analyses were consistent only with a single-stranded structure for the virus DNA. This was confirmed by the results of nearest neighbour base sequence analyses. Comparison of minute virus of mice with phage φX 174 and adeno-associated virus type 1 showed a close similarity of minute virus of mice and φX 174 and suggested that all three small DNA virus particles contain not more than 1.7 × 106 daltons of DNA.

Defective particles were the major product after undiluted passage of certain temperature-sensitive ( ts ) mutants of the Indiana C strain of vesicular stomatitis virus in BHK-21 cells at the permissive temperature (31 C). Essentially homogeneous preparations of defective particles were obtained with the wild-type and individual ts mutants. The defective particles associated with some of the ts mutants, however, were morphologically and physically distinguishable from wild type and from each other. All varieties of defective particle interfered with the multiplication of mutant and wild-type virus at the permissive temperature at early times of infection but failed to complement virions of different complementation groups at the restrictive temperature (39 C) at any time during infection.