First RNA polymerase was discovered by Severo Ochoa and Marianne Grunberg-Manago in 1955. Severo Ochoa and Sanae Mii continued this work; they purified RNA polymerase in 1961. In their research, they mentioned that the best preparations represent a 500-fold purification of the enzyme from the initial extracts. However, they are largely, although not totally, devoid of nuclease activity. RNA polymerase catalyzes the initiation (site selection), elongation and termination of polyribonucleotide chains, using ribonucleoside triphosphates as substrates and DNA as template. RNA polymerases from different prokaryotic sources are remarkably similar in subunit size and composition. RNA polymerase is sharply distinguished from DNA polymerase by its capacity to both start and terminate a chain when copying a duplex template. DNA polymerase, by contrast, cannot start chains and generally rely on transcription by an RNA polymerase or primase to do it for them. E. coli RNA polymerase is a multi-subunit protein with five distinct polypeptide subunits. It has Two copies of the subunit, along with one each of , ', , and , giving an molecular weight of about 450,000 Da for the holoenzyme. It is not required for the reconstitution of active enzyme.
Ochoa, S. and Mii, S. J. Biol. Chem. 236 (1961) 3303-3311