Viral Nucleic Acid Synthesis Research Articles

Interference of actinomycin D with the replication of the herpes virus DNA. I. Difference in behaviour of cellular and viral nucleic acid synthesis following treatment with actinomycin D

The rate of synthesis of DNA in HeLa cultures treated with small doses (0.5 μg/ml) of actinomycin D for 30 min is only depressed for a limited period of time: 6 h after the addition of the drug, DNA and RNA metabolism in the cell recover and quickly reach the control level. Herpes simplex virus-infected cells show the same phenomenon if treated with the antibiotic not later than 1 h after infection. Equilibrium sedimentation experiments in a CsCl gradient show that viral DNA replication is prevented if the drug is added during the first 6 h after infection, or irreversibly blocked if added during the following phase of viral DNA replication. Thus, the recovery of the DNA synthesis is limited to cellular DNA. It is concluded, therefore, that actinomycin D in appropriate doses preferentially inhibits herpes virus DNA replication.

The participation of DNA in Rofs sarcoma virus production

Experiments are presented showing that the inhibition by actinomycin D of Rofs sarcoma virus production, which was reported previofsly ( Temin, 1963b), is due to the inhibition of synthesis of viral nucleic acid. The results of experiments on the effects of amethopterin on Rofs sarcoma virus (RSV) production, on the induction of converted nonvirus-producing Rofs cells, and on the infection of normal cells with RSV are presented. There appear to be some steps in infection which are sensitive to inhibition by amethopterin which are not present in virus production or induction.

The Multiplication of Poxvirus DNA

It is no exaggeration to say that virtually all the concepts which together constitute the current model of virus replication are derived from work with the T-even bacteriophages. These include virus eclipse, now known to be due to uncoating of viral nucleic acid; more or less complete replacement of the host genome as a source of messenger RNA by the viral genome; and independent synthesis of viral nucleic acid and protein subunits followed by their combination culminating in virus maturation and release. Indeed, the case for working with a phage, T-even or some other, rather than with an animal virus appears overwhelming at first sight. Yet such a view would ignore the value of comparative studies. In fact, work with animal viruses has contributed considerably to our understanding of virus replication. Often this contribution has been merely to emphasize that the T-even phages are structures very highly adapted for infecting...

Virus infection and other factors affecting ribonuclease activity of plant leaves.

Abstract Rubbing of bean ( Phaseolus vulgaris L.) leaves, partial dehydration of cowpea [ Vigna sinensis (L.) Endl.] leaves, and inoculation of bean leaves with inactivated or viable pod mottle virus or of Datura stramonium L. leaves with tobacco mosaic virus resulted in increased ribonuclease activity of such leaves. The response after rubbing was more pronounced when the leaves were dusted with Carborundum prior to rubbing and when the medium contained Cu ++ or Zn ++ ions. The reaction was first noticeable approximately 2 hours after rubbing, reached its highest level 1 day after rubbing, and lasted for several days. Spraying of unwounded leaves with solutions of CuSO 4 also led to increased ribonuclease activity. Virus-infected leaves maintained higher levels of ribonuclease activity than healthy control leaves or leaves inoculated with inactivated virus. The effect of rubbing was not restricted to the upper epidermis, but extended into the mesophyll. Neither phosphatase nor phosphodiesterase activity significantly increased in bean or Datura leaves after rubbing of the leaves or after inoculation with virus. It is concluded that increased ribonuclease activity is not a specific response to virus infection, but occurs as a general shock reaction. In bean leaves with high ribonuclease activity, more lesions were produced and more pod mottle virus was synthesized than in leaves with lower ribonuclease activity. However, stimulation of ribonuclease activity by rubbing of bean leaves did not lead to increased pod mottle virus lesion formation or to stepped-up virus synthesis. The significance of these results is discussed with respect to a possible role of ribonuclease in the synthesis of viral nucleic acid.