INHIBITION OF DNA-SYNTHESIS IN BHK CELLS INFECTED WITH WESTERN EQUINE ENCEPHALITIS-VIRUS .2. PROPERTIES OF THE INHIBITORY FACTOR OF DNA-POLYMERASE INDUCED IN INFECTED-CELLS

Infection of baby hamster kidney cells with western equine encephalitis virus results in rapid inhibition of cellular DNA synthesis. We previously reported that an inhibitory factor of cellular DNA polymerase activity was found in infected cell extracts. The mechanism of this inhibitory action was studied by varying the amount of each component involved in the DNA polymerase reaction mixture. Increase in DNA polymerase or template DNA showed no effect on the inhibitory activity, whereas that in substrate deoxynucleotides markedly suppressed the inhibition. Accordingly, the target of the inhibitory factor may be deoxynucleotides, and the factor was expected to be a phosphohydrolytic enzyme. In fact, deoxynucleotides were markedly hydrolyzed in the reaction mixture incubated with the inhibitory factor. This phosphohydrolytic enzyme activity was identified as a nucleoside triphosphate phosphohydrolase, which had little specificity to the base or the sugar of nucleotides, but high specificity to the triphosphate moiety. This enzyme showed the maximal activity at pH 7.5, and required a low concentration of Mg2+, which could not be replaced by Mn2+ or Ca2+. Monovalent cations were not required. Furthermore, the enzyme activity was strikingly enhanced by addition of nucleic acids. The significance of this unique enzyme induced in infected cells is discussed in relation to inhibition of cellular DNA synthesis and viral replication. © 1979.