The effect of pseudorabies virus on the nucleic acid metabolism and on the nuclei of rabbit kidney cells

The changes in nucleic acid were followed in rabbit kidney (RK) cells infected with pseudorabies (Pr) virus.Infected cells, which had been suspended with Versene, centrifuged, and resuspended before acid precipitation, showed an increase of 85% in the ratio of deoxyribonucleic acid (DNA) to protein after 6 hours of incubation. This ratio was found to be overestimated by this method because of a loss of protein inherent in this technique. When the suspended cells were precipitated without previous sedimentation, the ratio of DNA to protein was 25% higher than that of the noninfected cells at 6 hours and 35% higher at 9 hours. Measurements of the absolute amount of DNA per sample showed that these increases are real.Pr virus appears to stimulate the proliferation of the nuclei of RK cells. This proliferation was demonstrated by an increase in the number of nuclei per sample by a factor of 1.93 in 6 hours and is reflected by the nuclei to cell ratio of 1.50 in 4 hours, a time when the cells have not yet coalesced to form syncytia. These results were corroborated by the finding that although there was an increase in the amount of DNA per cell, the amount per nucleus did not increase.Monolayers X-ray irradiated before infection showed no increase in DNA nor in the number of nuclei. The rate of virus synthesis, as well as the time of appearance of syncytia and of intranuclear inclusions, was the same as in the nonirradiated controls. These results suggest that the newly synthesized DNA may be cellular and not viral.