DNA-Dependent RNA Polymerase Activity Associated with Subviral Particles of Polyhedral Cytoplasmic Dexoyribovirus

Abstract

Polyhedral cytoplasmic deoxyribovirus virions contain a DNA-dependent RNA polymerase which catalyzes the incorporation of ribonucleotides into an acid-precipitable product. Treatment of virions with sodium deoxycholate and dithiothreitol resulted in the formation of subviral particles which could be separated from virions by rate zonal centrifugation in sucrose gradients. Subviral particles were RNA polymerase-positive and more active per unit mass of protein than virions. In vitro enzyme activity associated with subviral particles required addition of ribonucleotides, Mg 2+ , and exogenous denatured DNA template. Optimal enzyme activity occurred over a broad pH (7.2 to 8.8) and Mg 2+ concentration (2 to 10 μmol) range. The specific activity of the RNA polymerase was maximal at 37 C. Addition of DNase or actinomycin D to the reaction mixture reduced the incorporation of [ 3 H]UMP into an acid-precipitable product. The product of the reaction was sensitive to degradation by RNase but not to DNase or Pronase. These data suggest that the enzyme copies DNA into RNA.