Purification of deoxyribonucleic acid polymerase delta from calf thymus: partial characterization of physical...

Deoxyribonucleic acid (DNA) polymerase delta has been purified 7800-fold from calf thymus, to a specific activity of 28 000 units/mg of protein. Similar to DNA polymerase delta from bone marrow [Byrnes, J.J., Downey, K. M., Black, V. L., & So, A. G. (1976) Biochemistry 15, 2817], the calf thymus enzyme is associated with 3'- to 5'-exonuclease activity. Both DNA polymerase and 3'- to 5'-exonuclease activities copurify on hydroxylapatite, DNA-cellulose, and molecular sieve chromatography. The ratio of exonuclease activity to polymerase activity is approximately 1:12. When the most highly purified fraction is subjected to polyacrylamide gel electrophoresis under nondenaturing conditions, both DNA polymerase and exonuclease activities have the same mobility at several acrylamide gel concentrations. Isoelectric focusing experiments have shown that both activities have the same pI. These data suggest that 3'- to 5'-exonuclease activity is an intrinsic property of DNA polymerase delta. The molecular weight of the enzyme, as estimated from measurements of Stokes radius and sedimentation coefficient, is 152 000.