Proliferating cell nuclear antigen (PCNA) and PCNA-dependent DNA polymerase δ were partially purified and characterized from rabbit bone marrow. Rabbit DNA polymerase δ sediments at 8 2 S upon glycerol density gradient centrifugation. Similar to calf thymus PCNA-dependent DNA polymerase δ, a 125-123-kDa doublet and 48-kDa polypeptides correlate with DNA polymerase activity. Western blotting of rabbit DNA polymerase δ with polyclonal antibody to calf thymus PCNA-dependent DNA polymerase δ gives the same results as calf thymus δ; the 125-123-kDa doublet is recognized. PCNA-dependent DNA polymerase δ is resistant to inhibition by dideoxynucleotides and is relatively insensitive to inhibition by N2[p-(n-butyl)phenyl]dGTP. A 3′→5′ exonuclease copurifies with the DNA polymerase. The processivity of DNA polymerase δ alone is very low but greatly increases with the addition of PCNA from rabbit bone marrow or calf thymus. Comparative studies of the original DNA polymerase δ from rabbit bone marrow demonstrate a lack of recognition by antibodies to calf thymus δ and a high degree of processivity in the absence of PCNA. Additionally, the originally described DNA polymerase δ is a single polypeptide of 122 kDa. These features would recategorize the original δ to the ε category by recently proposed convention. PCNA-dependent DNA polymerase δ is a relatively minor component of rabbit bone marrow compared to DNA polymerase α and PCNA-independent DNA polymerase δ (ε), the relative proportions being α, 60%; δ, 7%; and ε, 30%.
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