Purification and Subunit Structure of Deoxyribonucleic Acid-dependent Ribonucleic Acid Polymerase III from the Mouse Plasmacytoma, MOPC 315

Class III DNA-dependent RNA polymerases were purified from the mouse plasmacytoma, MOPC 315. RNA polymerases IIIA and IIIB were solubilized from a whole cell extract and resolved by chromatography on DEAE-Sephadex. Chromatography on DEAE-cellulose, DEAE-Sephadex, CM-Sephadex, and phosphocellulose ion exchange resins and sedimentation in sucrose density gradients yielded chromatographically homogeneous Enzymes IIIA and IIIB which were purified approximately 22,000 and 53,000-fold respectively, relative to whole cell extracts. The specific activity of these enzymes was comparable to that reported for other purified eukaryotic RNA polymerases. Sucrose gradient sedimentation analysis suggested a molecular weight of approximately 650,000 for each of the class III enzymes.