Three forms of DNA polymerase, named enzymes A, B, and C, that preferred (rA)n•(dT)12-18 as a template-primer, were partially purified from an extract of rat spleen. Enzymes B and C, both sedimenting at 9 S, appeared to correspond to DNA polyrnerase γ. However, they differed in their behavior on phosphocellulose and DNA-cellulose column chromatographies, and in their optimum KCl and divalent cation requirements for activity.
Enzyme A showed a unique property. Like DNA polymerase β, it sedimented at 3.8 S, was resistant to reagents blocking sulfhydryl groups, and was inhibited by phosphate, but it differed from DNA polymerase β with respect to elution positions from DEAE-cellulose, phosphocellulose and DNA-cellulose columns, K_m value (lower by one order of magnitude for dTTP), and template-primer preference. Enzyme A was found in the mitochondrial fraction, in which DNA polymerase β was not detectable.
Enzymes A and C were isolated from the nuclear fraction, but this fraction did not contain enzyme B. The cytosol contained only enzyme A. The mitochondrial fraction contained enzyme A and enzyme C-like polymerase. Enzyme B was obtained with enzymes A and C only by extraction of the whole cell homogenate. Enzyme B may be labile or may be an artificial form of DNA polymerase γ formed during the purification procedures.