Animal DNA‐Dependent RNA Polymerases

Calf thymus AI DNA‐dependent RNA polymerase was purified by chromatography on phosphocellulose, Sepharose 6B and DEAE‐Sephadex and by glycerol density‐gradient centrifugation. The polymerase was more than 90% pure and free of contaminating nucleases. Addition of 30% glycerol to all buffers increased the stability of the enzyme activity throughout the purification, but the final yield of activity was nevertheless low. This does not seem to be due to the loss of a stimulating factor during the purification. No evidence was found for an enzyme resembling rat liver AII DNA‐dependent RNA polymerase in calf thymus.