DNA-dependent RNA polymerases from Acanthamoeba castellanii. Multiple forms of the class III enzyme and levels of activity of the polymerase classes during encystment.

Multiple forms of class III DNA-dependent RNA polymerase have been found in a number of higher eukaryotic cells types (Chambon, P. (1975) Annu. Rev. Biochem. 44, 613--638). Similar multiple forms are reported here from a lower eukaryote, the soil amoeba Acanthamoeba castellanii. The levels of activity of all three RNA polymerase classes in whole cell extracts of Acanthamoeba during cellular differentiation were examined. In contrast to our previous observation (Detke, S. and Paule, M.R. (1975) Biochim. Biophys. Acta 383, 67--77) that the amount of the alpha-amanitin-sensitive polymerases (II + III) increase in the nucleus during encystment we find that the amount of polymerases II and III when solubilized from whole cells remains constant. The level of activity of polymerase I, however, remains constant both in nuclei and in whole cell extracts. Thus, the shutdown of ribosomal RNA synthesis occurring during encystment is not due to a decrease in the number of polymerase I molecules in the cell.