Cell cycle-dependent variations in RNA polymerase activity in the nuclear and cytoplasmic fractions of Physarum polycephalum.

The RNA polymerase activities of the soluble enzymes from the nuclear and cytoplasmic fractions from synchronous macroplasmodia of Physarum polycephalum were measured. Activity in the nuclear fraction prepared from cells in the G2 phase was several times higher than that at metaphase, and activity in the cytoplasmic fraction was much higher at metaphase than in the G2 phase. The amount of activity was nearly constant during the late G2 phase and early prophase, then rose abruptly just before metaphase, becoming tenfold higher at metaphase then decreasing rapidly during anaphase-telophase. The cytoplasmic activity at metaphase was attributed almost exclusively to the type II (or B) enzyme as shown by alpha-amanitin inhibition and chromatographic analysis of the enzyme. Results indicate that at metaphase RNA polymerase II molecules are loosely associated with condensed chromosomes or that they move from the mitotic nuclei into the cytoplasm.