DNA-dependent RNA polymerase I from hepatomas: comparison of activity levels and properties

Activity levels of DNA-dependent RNA polymerase I (Pol I; ribonucleoside triphosphate: RNA ribonucleotidyl transferase, E.C. 2.7.7.6, eucaryotic type I) have been compared in five transplantable murine hepatomas and livers of three inbred mouse host strains. Three tumors (H6, H4 and H134) contained about 350-450 units of Pol I activity/g of tissue. Two hepatomas (H129 and BW7756) contained about 120-150 units of activity/g of tissue. Livers contained about 100-150 units/g of tissue. Chromatographic comparisons revealed that hepatoma Pol I is slightly less anionic than the liver enzyme. Thermal denaturation studies were carried out using Pol I partially purified from a high-activity line hepatoma (H6), a low-activity line hepatoma (H129) and livers of the appropriate host strains. Pol I from H6 tumors was denatured at 40 degrees C with a half-time of 2 min. The enzyme from H129 tumors and host livers was denaturated with a half-time of 7 min. These data indicate that hepatoma H6 expressed a structural variant of Pol I. This is the first Pol I variant ever reported.