A new mammalian DNA polymerase with 3' to 5' exonuclease activity: DNA polymerase δ

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Abstract
A new species of DNA polymerase was purified more than 10,000-fold from the cytoplasm of erythroid hyperplastic bone marrow from rabbits. This DNA polymerase, in contrast to previously described eukaryotic DNA polymerases, is associated with a very active 3'' to 5'' exonuclease activity. Similar to the 3'' to 5'' exonuclease activity associated with prokaryotic DNA polymerases, this enzyme catalyzes the removal of 3''-terminal nucleotides from DNA, as well as a template-dependent conversion of deoxyribonucleoside triphosphates to monophosphates. The exonuclease activity is not separable from the DNA polymerase activity by chromatography on DEAE-Sephadex or hydroxylapatite, and upon sucrose density gradient centrifugation the 2 activities cosediment at 7 S [svedburg units] or at 11 S depending on the ionic strength. Both exonuclease and polymerase activities have identical rates of heat inactivation and both are equally sensitive to hemin and Rifamycin AF/013, inhibitors of DNA synthesis that act by binding to DNA polymerase and causing its dissociation from its template/ primer. This suggests the coexistence of 2 enzyme activities in a single protein.

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