Stimulation of RNA synthesis in nucleoli by inorganic phosphate in vitro

The biological function of a phosphoprotein with a molecular weight of 120 000 daltons localized in the nucleoli of mouse ascites sarcoma cells was studied by examining the effect of the phosphoprotein on RNA synthesis in the nucleoli in vitro. The phosphoprotein did not stimulate ribosomal RNA synthesis in vitro. During this study, it was observed that inorganic phosphate enhanced RNA synthesis in the nucleoli in vitro in the presence of either Mn²⁺ or Mn²⁺ plus Mg²⁺ as divalent cations. Inorganic phosphate stimulated the rate of the chain elongation reaction in RNA synthesis.