In vitro synthesis of a high molecular weight virion-associated RNA by vaccinia.

Although the bulk of RNA synthesized in vitro by vaccinia virus is 8 to 12 S, a small amount of high molecular weight RNA can be detected. This RNA is virion-associated and is not extruded from the virus as high molecular weight RNA. It is sensitive to pancreatic RNase digestion in high salt, has a density in neutral CS2SO4 of 1.68 g ml-1 and remains large after digestion with DNase or denaturation in dimethyl sulfoxide. In the presence of high concentrations of virus in the in vitro RNA polymerase reaction, pulse-labeling experiments indicate an RNA sedimenting heterogeneously between 20 and 30 S. Pulse-chase experiments indicate that a fraction of this high molecular weight RNA can be chased into RNA sedimenting at 8 to 12 S. Cleavage into smaller fragments is not dependent on continued RNA synthesis but does require ribonucleoside triphosphates. In the presence of ethidium bromide, the RNA is not cleaved.