Control of Certain Aspects of the Infective Process by Progeny Viral DNA

Light sensitive halogenated isomers (FU, BUDR) replace thymidine affects form but not function of viral progeny. Enzyme cutoff is inhibited. Puromycin remediates this.

When rabbit kidney cells infected with pseudorabies virus are incubated with 5- fluorouracil (FU) and 5-bromodeoxyuridine (BUDR), approximately 80% of the thymidine in the progeny viral DNA is replaced by BUDR. These conditions do not affect the initial increase of enzymatic activity and of DNA synthesis in the infected cells. However, the drug prevents the normal cutoff of enzyme synthesis which occurs by 6 hours after infection. BUDR also delays the loss of enzymatic activity that takes place between 10 and 14 hours after infection. The loss of enzyme activity, which occurs during the late stages of the infective process, seems to result from the leakage of cellular constituents, including enzymes, from the cells. Specific proteins, which are synthesized by the infected cells between 4 and 7 hours after infection, are responsible for this leakage. BUDR interferes with the formation, not with the function, of these proteins. The results of the experiments presented are consistent with the idea that incorporation of BUDR into progeny viral DNA interferes with some of the aspects of the infective process controlled by this DNA.

"That leakage from the cell is not correlated with the formation within the cells of infectious virus or viral coat proteins is concluded from the following facts: (1) The addition of puromycin to infected cells at any stage of the infective process inhibits, as expected, the subsequent formation of infectious virus; the antibiotic, however, affects leakage from the cells only when added during the early stages of the infective process. (2) The proteins responsible for leakage first appear at approximately 4 hours after infection; viral coat proteins, on the other hand, start being synthesized at 2.5 hours after infection (Hamada and Kaplan, 1965). (3) Leakage is retarded in BUDR-treated infected cells as compared to thymidine-treated infected cells; BUDR-treated infected cells, however, synthesize viral coat proteins and form viral particles at approximately the same rate as the thymidine-treated infected cells (Kaplan et al., 1965). However, it should be pointed out that the viral proteins synthesized in the drug-treated cells may, of course, differ somehow from normal viral proteins. " (Emph. mine - rjs)