Structure of monkey kidney cell RNA polymerase II: characterization of RNA polymerase associated with SV40 late transcriptional complexes.

Three subspecies of RNA polymerase II have been described in eucaryotic cells and designated IIO, IIA, and IIB. Although their relative proportions vary among different sources, RNA polymerases IIA and IIB constitute the bulk of most purified RNA polymerase II preparations. Antibodies against calf thymus RNA polymerase II were used to estimate the amount of polymerase II subspecies in monkey kidney cells, isolated nuclei, and SV40 late transcriptional complexes. We have found that RNA polymerase IIO is present in whole cells and isolated nuclei in higher proportions than previously reported. Subspecies IIO was found associated with SV40 minichromosomes engaged in transcription during late lytic infection. The observation that RNA polymerase IIO is associated with the cellular chromatin and SV40 minichromosomes suggest that this form of the enzyme is the subspecies active in in vivo transcription.