Multiple Forms of Deoxyribonucleic Acid-dependent Ribonucleic Acid Polymerase in Xenopus laevis

RNA polymerase activity was solubilized from whole cell homogenates of cultured kidney cells and embryonic tissues of Xenopus laevis. Several chromatographic forms of RNA polymerase were distinguished in extracts from all tissues by ion exchange chromatography and are designated Ia, Ib, IIa, IIb, and III. Forms Ia and/or Ib, IIb, and III appear analogous to forms I, II, and III isolated from nuclei of other eukaryotes, whereas form IIa may be of cytoplasmic origin. The metal ion and ionic strength responses of each of the enzymes were examined. No differences were noted between Ia and Ib on the one hand, or between IIa and IIb the other. However, class I, II, and III enzymes were distinguishable by these criteria. Forms IIa and IIb were equally sensitive to α-amanitin, whereas the activities of forms Ia, Ib and III were unaffected by this toxin.