Calf thymus RNA polymerases I and II do not contain subunits structurally related to casein kinases I and II.

Both calf thymus RNA polymerases I and II contain small subunits of molecular weight nearly identical with the subunits of casein kinases II and I, respectively. Antibodies prepared against calf thymus casein kinase II react with the Mr = 44,000 and 26,000 subunits of protein kinase but do not react with the Mr = 44,000 and 25,000 subunits of RNA polymerase I. These RNA polymerase I and casein kinase II subunits were purified by polyacrylamide gel electrophoresis, labeled with 125I and peptide maps generated. The tryptic peptide map of neither the Mr = 44,000 nor the 25,000 subunit of RNA polymerase I resemble the map obtained for the subunits of similar size in casein kinase II. The peptide maps generated from the Mr = 25,000 subunits of RNA polymerases I and II are, however, identical. Calf thymus RNA polymerase I, prepared by standard procedures is contaminated with casein kinase II which can be removed by rechromatography on DEAE-Sephadex. Antibodies prepared against calf thymus protein kinase I also fail to interact with the RNA polymerase II subunit of comparable size. Furthermore, peptide maps indicate that these subunits are not structurally related.