Multiple Nuclear Ribonucleic Acid Polymerases during Development of Dictyostelium discoideum

DNA-dependent RNA polymerase activity was extracted from nuclei of Dictyostelium discoideum at two stages in the life cycle: during exponential growth and during differentiation into fruiting bodies. The activity from both stages could be resolved into several fractions which differed in sensitivity to α-amanitin and in ionic requirements. No significant change in the proportions of the various fractions was found during development. Both polymerases I and II, isolated from either growing or differentiating cells, were found to prefer double-strand DNA of D. discoideum but could also use DNA from a variety of organisms to a lesser extent. No change in template specificity was observed during development. Polymerase II was purified to apparent homogeneity from both growing and differentiating cells and the subunit composition determined by acrylamide gel electrophoresis in the presence of dodecyl sulfate. Five protein subunits were consistently observed with approximate molecular weights of 170,000, 150,000, 28,00o, 21,000, and 15,000. Although a 190,000 molecular weight subunit was observed in certain preparations from growing cells, it was not found to be an obligatory component of the enzyme. These studies suggest that the change in the pattern of transcription which occurs during development in D. discoideum may depend on factors other than alteration of RNA polymerase.