A cytoplasmic DNA polymerase has been purified 200fold from erythroid hyperplastic bone marrow. This enzyme shows an absolute requirement for a divalent cation, which may be either Mg2+ or Mn2+, and is stimulated about fourfold by a monovalent cation, NH4+ or K+. The enzyme preferentially uses activated calf thymus DNA and poly[d(A-T)] as a template, while native calf thymus DNA and synthetic DNA/RNA hybrids are rather poor templates. DNA synthesis with this enzyme is inhibited by low concentrations of heme or ethidium bromide. The rate of DNA synthesis with the cytoplasmic DNA polymerase is markedly dependent on pH as well as the concentrations of divalent and monovalent cations and the effects of these factors are interdependent and interrelated. Changes in pH have profound effects on the concentration of monovalent and divalent cations required for optimal activity and, conversely, changes in the concentrations of divalent and monovalent cations also influence the optimal pH of the reaction. The mechanism of salt activation has been shown to involve a dissociation of the DNA polymerase from an 11,6-S dimer to an 8-S monomer.
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