[Dependence of RNA synthesis in the cell of Physarum polycephalum on concentration and activity of RNA-polymerase II].

The RNA synthesis detected by incorporation of [H3]uridine chase label proceeds in macroplasmodium and in isolated nuclei throughout the cell cycle of a synchronous myxomycetes culture of Physarum polycephalum, producing two well-shaped peaks at the postmitotic and premitotic steps. Such RNA synthesis is due to the activity of alpha-amanitin-sensitive RNA-polymerase II. Concentrations of RNA-polymerase II at various steps of the cell cycle were determined by alpha-amanitin titration; the specific activity of the enzyme was assayed. The increase in the rate of mRNA synthesis was accompanied by a rise in the concentration and specific activity of the enzyme: for the postmitotic peak, for instance, the corresponding values were about 2-2.5 and 2-4 times as high as minimum values revealed during the cycle. The results obtained are discussed in terms of transcription control in eukaryotic systems.