title: The relationship between the activity of DNA-dependent RNA polymerase I and the rate of synthesis of rRNA in hepatoma cells in culture.
abstract: Cell culture lines were established from the transplantable mouse hepatomas H6 and H129. Both cell lines had a doubling time about 30 h when maintained in medium containing 5% foetal bovine serum. H6 cells contained about 3-4 times more DNA-dependent RNA polymerase I (Pol I; ribonucleoside triphosphate--RNA nucleotidyltransferase, EC 2.7.7.6) than did H129 cells. Moreover, the H6-cell enzyme was more heat-labile than that from H129 cells. Steady-state contents of 28S rRNA were measured in both cell lines. Exponentially growing cultures of H6 cells contained about 6.5pg of 28S rRNA/cell, and similar cultures of H129 cells contained about 5.8pg/cell. Stationary cultures of both cell lines contained about 2pg of 28S rRNA/cell. By two different techniques, the half-time for turnover of 28S rRNA was estimated to be 16-17h for both H6 and H129 cells. Knowing the turnover rate and the steady-state concentration, one may calculate that both H6 and H129 cells synthesize 28S rRNA at a rate of about 0.25 pg/h per cell. The amount of template-bound Pol I activity was similar in nuclei isolated from H6 and H129 cell cultures. These data indicate that, although H6 cells contained 3-4 times more Pol I than did H129 cells, both cell lines synthesized rRNA at about the same rate.
mesh_terms: D000818:Animals; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D007700:Kinetics; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D008715:Methionine / Q000378:metabolism; D051379:Mice; D011489:Protein Denaturation; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis*
chemical_list: D012335:RNA, Ribosomal; D004247:DNA; D008715:Methionine; D012321:DNA-Directed RNA Polymerases; D012318:RNA Polymerase I