- Volume 6, Issue 3, 1970

A membranous cell-free system derived from Escherichia coli is described. When the system is primed with λ bacteriophage DNA, the RNA synthesized by the system hybridizes specifically with λ DNA. The primed system is also capable of synthesizing active phage lysozyme.

Neurovaccinia virus propagated in the presence of bromodeoxyuridine loses the capacity to produce necrosis in the skin of rabbits. Mechanisms underlying this loss were studied. The population under study consisted predominantly of virus particles capable of producing necrosis (RS+) and a small portion of particles which had lost this capacity (RS− ). An RS− clone isolated from the population induced an inhibitor of interferon type in rabbit skin, which markedly inhibited reproduction of RS+ virus strains and consequently the capacity of these strains to produce necrosis.

Residual infectivity detected after the interaction of Venezuelan equine encephalomyelitis virus with specific antiserum was caused mainly by the formation of infective virus + antibody complexes (sensitized virus) that could be neutralized by serum containing antigamma globulin (IgG). The quantities of virus sensitized by antiserum to Venezuelan equine encephalomyelitis and neutralized by anti-IgG serum depended on the antibody concentrations of these sera. In contrast to the marked temperature and time-dependence of Venezuelan equine encephalomyelitis virus neutralization by antiserum, neutralization of sensitized virus by anti-IgG serum was more rapid, being almost complete within 1 min. at 35°, and less sensitive to temperature. Virus sensitization preceded neutralization and indicated that infective virus + antibody complexes were formed before virus neutralization began. The neutralization of sensitized virus by anti-IgG serum was generally species specific. Differences in the ability of anti-IgG, anti-IgA, and anti-IgM sera to neutralize sensitized virus indicated that the reaction was also influenced by the class specificity of the anti-immunoglobulin.

Sensitized virus was partially neutralized by goat antiserum to monovalent Fab fragments of human IgG and, to a lesser degree, by the Fc fragment. Sensitized virus was neutralized by an in vitro mixture of these fragments to almost the same degree as by goat antiserum to intact human IgG. The Fc fragment may, therefore, by involved in virus neutralization.

The RNA content of encephalomyocarditis virus was found to be 31·7 %, a figure obtained by combining results from nitrogen and phosphorus determinations which gave 32·0 %, from extinction measurements at 260 nm. on perchloric acid hydrolysates which gave 31·3% and from orcinol determinations which gave 31·8%. Specific extinction coefficients obtained were E1 em 1%. at 260 nm. = 77·4 for the virus in 0·1 m-KCI+ 0·02 m-phosphate buffer, pH 8·0, and E1 cm 1% at 260 nm.= 221 for its RNA in 0·0 m-tris + HCl, pH 7·2.

A particle weight of 8·50 × 106 for encephalomyocarditis virus was derived by combining results from (a), sedimentation velocity measurements on highly purified preparations of virus (0·1 to 5 mg./ml.) in 0·1 m-KCl + 0·02 m-phosphate buffer, pH 8·0, which gave an of 162·3 s, (b), differential sedimentation studies of virus in the same solvent but containing various ratios of D2O to H2O which gave a partial specific volume of 0·678 ml./g., with results from (c), analysis of boundary spreading during low speed centrifugation of dilute virus solutions which led to a diffusion coefficient D 20,w of 1·44 × 10 −7 cm.2/sec. Sedimentation equilibrium studies on similar virus preparations in the same solvent gave a particle weight of 8·52 × 106. This suggested a hydrated particle diameter for the virus of 29·8 nm. and a frictional ratio f/fo of 1·130 which was consistent with that of a hydrated sphere containing 0·29 g. water/g. dry virus.

A nocardiophage, called Ri, was isolated from soil samples. It lysed Nocardia restrictus and a few other species of Nocardia, but none of the eight streptomycetes tested. On N. restrictus phage Ri produced plaques very irregular in shape, size and turbidity; replacement of NaCl by Ca(NO3)2 in the medium increased the uniformity of plaque morphology and gave higher counts. Electron microscope examination of the phage particles revealed a hexagonal head, 75 nm. in diameter, and a long, flexible, non-contractile tail, 330 × 10 nm., bearing a round terminal plate; a collar was sometimes visible in particles with empty heads. The phage nucleic acid is most probably double-stranded DNA. Maximum viability of phage was at pH 7; the survival was less than 0·001 % for an exposure of 30 min. at pH 5; about 20% survived at pH 6, and 10% at pH 8. When exposed to 55° or to ultraviolet irradiation, phage Ri showed similar survival curves, and was very sensitive to both treatments. Adsorption of phage to its host was rapid and efficient (80% in 5 min.); the latent period was 28 min., the rise period occurred between 28 and 37 min., and the burst size was 61. Mutation of N. restrictus to resistance to phage Ri was very rare; the apparent mutation rate was 3·4 × 10−11, which can be partly attributed to the lower growth rate of the resistant mutants. In chromium-shadowed preparations, N. restrictus appeared as short rods, 1·3 × 0·5 μ., dividing by transverse fission, showing no lateral branching characteristic of the genus Nocardia, and very few chains (never longer than 2 or 3 cells); thin sections of infected cells showed a few intracellular phage particles.

The neuraminidases and haemagglutinins of 20 isolates of swine influenza virus collected between 1930 and 1967 were compared in neuraminidase-inhibition and haemagglutination-inhibition serological tests. All the isolates were serologically related to a greater or lesser extent in tests with either antigen. The antigenicity of the two antigens varied independently in different isolates. There was a slight, but statistically significant, drift in the antigenicity of both antigens during the period in which the isolates were collected.

Bacteriophage-like particles were induced from 6 of 21 strains of stalked bacteria, using mitomycin C or ultraviolet irradiation as the inducing agents. The phage inductions were observed in strains of Caulobacter crescentus, C. vibrioides and C. bacteroides. The phage-like particles were observed, using electron microscopy. Two of the phage-like entities, tentatively designated defective phages, could not be propagated on any of 21 potential host strains tested, nor did they possess bacteriocin activity. Host strains which permitted lytic cycles of phage replication were found for four induced phages.These bacteriophages contained double-stranded DNA. The bacterial strains from which they were induced were [resistant to infection by their respective phage. Four bacterial strains were treated with specific antiphage serum, but clones so treated retained their capacity to produce the phages. The inefficacy of antiphage serum in curing the bacteria of phage suggested that these Caulobacter strains were lysogenic.

Imaginal discs from Drosophila larvae infected with sigma virus by paternal inheritance were implanted in adult hosts to measure their infectivity. The number of infective imaginal discs was lower than the number of infected adults after imaginal emergency.