Products of RNA polymerases in HeLa cell nuclei

RNA polymerase activities in intact HeLa cell nuclei have been examined and compared to activities investigated in previous studies of the purified enzymes. The RNA synthesized by the mammalian polymerases while still in nuclei is identified. The polymerases are tentatively identified by location, sensitivity to alpha-amanitin, and response to manganese and altered ionic strength. Polymerase I is located in the nucleolus and labels partially complete precursor molecules of ribosomal RNA. Polymerases II and III are in the nucleoplasm and both label giant nuclear heterogeneous RNA.