On the role of ribonucleic acid in animal virus synthesis. II. Studies with ribonuclease

Observations on the fine structure of mature herpes simplex virus and on the composition of its nucleoid

The fine structure and composition of mature herpes virus have been investigated in thin sections by electron microscopy. The virus was grown in cultured HeLa cells and was collected with them. Tests for the biological activity of the infected cultures were included in the first half of the work. Preparations were fixed with both osmium and permanganate, and were embedded either in methacrylate or in aquon, a water-miscible fraction of a commercially available epoxy resin. In further experiments material fixed with permanganate was subjected to the action of specific nucleases or control medium before embedding. All the preparations showed numerous uniform particles around and between the cells and this was paralleled by considerable biological activity where tests were made on samples of the culture fluids. Mature herpes virus has been found to be round and to measure, when dehydration shrinkage is avoided, about 165 mmicro in diameter. The particle contained an eccentric round-ended rod-shaped, electron-opaque nucleoid lying in an inner zone of low density. A dense outer zone or viroplasm surrounded this, no membrane being present between the two zones. After permanganate fixation the particle was found to have an outer limiting membrane showing a triple-layered structure morphologically indistinguishable from that of the plasma membrane of the HeLa cells. The results of the digestion experiments show that herpes virus contains nucleic acid of deoxyribose type and that this is localized in the dense nucleoid. Both the findings and the methods used are discussed.

On the role of ribonucleic acid in animal virus synthesis. I. Studies with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole

Adenosine, but not guanosine, was capable of blocking the inhibitory effect of 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole (DRB) on influenza virus multiplication in the chorioallantoic membrane in vitro. At virus inhibitory concentrations DRB caused marked inhibition in uptake of adenosine-8-C¹⁴ into RNA of uninfected host cells, but it had little effect on uptake of C¹⁴-L-alanine into host cell proteins or on cellular oxygen consumption. The activity of DRB in inhibiting multiplication of the DNA-containing adenovirus was similar to its inhibitory activity on multiplication of the RNA-containing influenza virus. These and earlier results are discussed from the point of view of the important role of RNA in the reproduction of DNA-containing viruses.

Demonstration of the sequential development of vaccinial antigens and virus in infected cells: observations with cytochemical and differential fluorescent procedures

Virus-induced alterations in vaccinia virus-infected HeLa cells have been followed by immunofluorescent and cytochemical techniques. In a time sequence study, infected cells show an early increase in cytoplasmic RNA content, followed by appearance of centers of viral DNA synthesis in the cytoplasm. The centers of synthesis were detected at 4 hours post infection, with the acridine orange fluorochrome stain as compared to 6 hours with Feulgen and methyl green-pyronin stains. Marginal fragmentation of the inclusion bodies was seen at 8 to 10 hours post infection, and appears to coincide with the first increase in cell-associated virus. With the immunofluorescent technique, it was found that the LS antigen of the virus can be detected at about 4 hours post infection. This is followed at 5 to 6 hours post infection by the appearance of the NP antigen. Both antigens are found only in the cytoplasm, and precede the appearance of the infective particle. The HA antigen, a by-product of virus-cell interaction, is not seen until about 10 hours post infection; that is, several hours after the appearance of both the LS and NP antigens, and only after the appearance of mature virus. The successful application of the use of two immune sera, each labeled with a different fluorescent dye for the simultaneous visualization of two antigens within a cell, is reported. Using this technique, the sites of LS and NP antigen synthesis, were easily differentiated. The intimate mixing of the two antigens at a later stage appears to coincide with the fragmentation of the inclusion body and the first detectable increase in cell-associated virus. The evidence obtained strongly suggests that the typical inclusion body observed in vaccinia-infected cells is composed mainly of the NP antigen.

Pancreatic ribonuclease: enzymic and physiological properties of a cross-linked dimer

Monomeric ribonuclease A has very low activity toward typically double-stranded RNA's; the dimeric form of ribonuclease A obtained by cross linking the enzyme by dimethyl suberimidate has more than 78 times the activity of the monomer toward polyadenylate . polyuridylate and 440 times the activity of the monomer toward the double-stranded RNA of a virus from Penicillium chrysogenum. The half-life of the dimer in the bloodstream of the rat is 12 times that of the mononmer.

Infectious nucleic acids, a new dimension in virology

Viral nucleic acids have been found to be infectious for tissues and animals, yet are nonantigenic and resistant to antibodies against whole virus. Other unique properties, such as their host range and their susceptibility to nuclease action, render them a wholly new dimension to be reckoned with in virology. These properties may explain a number of conditions which at present are considered anomalous. The release from infected tissues of even a small proportion of total virus as free nucleic acid could, in an otherwise immune individual, lead to a low level of infection which would, perhaps, explain permanent immunity. If the proportion of nucleic acid is higher, or if the nucleic acid is resistant to nucleases because of an inert envelope, such conditions as "carrier" states-that is, viremias with or without antibodies-are possible. Note added in proof: The recent article by J. D. Ebert and F. H. Wilt (54) came to my attention after the present article was written. Ebert and Wilt's excellent article indicates the impact of the newer knowledge of viral nucleic acids on the ideas developing in the field of embryology.