title: Inhibitory effects of nucleoside triphosphates on nucleolar RNA synthesis.
abstract: Studies on the effects of substrates on RNA polymerase I [EC 2.7.7.6] in vitro showed that nucleolar RNA synthesis was inhibited by an excess of substrate nucleoside triphosphates in the presence of Mg2+. GTP and UTP were more inhibitory than CTP and ATP. These compounds specfically inhibited nucleolar RNA synthesis and a concentration of GTP that strongly inhibited nucleolar RNA synthesis did not inhibit RNA synthesis by partially purified RNA polymerase I. The inhibition of nucleolar RNA synthesis disappeared at pH 9.0 without any change in the apparent Km for GTP or the Vmax of RNA synthesis.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism*; D003570:Cytidine Triphosphate / Q000494:pharmacology; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D009711:Nucleotides / Q000494:pharmacology*; D012313:RNA / Q000096:biosynthesis*; D012318:RNA Polymerase I / Q000378:metabolism*; D012294:Rifamycins / Q000494:pharmacology; D014542:Uridine Monophosphate / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D002413:Cations, Divalent; D009711:Nucleotides; D012294:Rifamycins; D012313:RNA; D003570:Cytidine Triphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D014542:Uridine Monophosphate; D012321:DNA-Directed RNA Polymerases; D012318:RNA Polymerase I; D014544:Uridine Triphosphate