Studies on Deoxyribonucleic Acid Polymerases from Yeast

A mitochondria‐free cell extract from Saccharomyces cerevisiae was used as source of yeast DNA polymerase for the partial purification and characterization of the enzyme. Upon DEAE‐cellulose chromatography, the total DNA polymerase activity separates into a major fraction, DNA polymerase A, and a minor fraction, DNA polymerase B. The final purification achieved was 150‐to 200‐fold for DNA polymerase A and 60‐to 80‐fold for DNA polymerase B. The two polymerases A and B differ from each other in some properties. Both purified enzyme preparations contain only traces of nucleases and very little, if any, terminal transferase. Activity is totally dependent on the presence of DNA, all four deoxyribonucleoside triphosphates and Mg++. With “activated” DNA or with poly d(A‐T) as template the DNA polymerases A and B exhibit an optimal activity. Native DNA preparations promote DNA synthesis to a low degree only, while denatured DNAs are even less active as templates. The enzymes have a molecular weight around 150 000; however, larger aggregates have been observed under certain conditions.