Evidence that DNA Polymerase‐a of Calf Thymus Contains a Subunit of Molecular Weight 155000

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Abstract
Small samples of the 8-S species of enzymes (A1 and A2) occurring in the DNA polymerase-.alpha. (EC 2.7.7.7) fraction of calf thymus, were extensively purified using non-denaturing (normal) polyacrylamide gel electrophoresis. When peak fractions of activity on normal gels were subjected to dodecyl-sulfate-polyacrylamide gel electrophoresis, a polypeptide at 155,000 correlated with polymerase activity. Samples of the 7.3-S (C) enzyme prepared from A2 by treatment with 2.4 M urea or isolated directly without exposure to urea, also showed the presence of a 155,000-Mr polypeptide. The 7.3-S (C) enzyme, of previously estimated molecular weight 155,000-170,000, is a single polypeptide and that the 8-S enzymes A1 and A2 contain an additional subunit of 50,000-70,000 molecular weight.