AN INHIBITOR OF DNA POLYMERASE-ALPHA AND POLYMERASE-DELTA IN CALF THYMUS DNA

Most, although not all, samples of commercial calf thymus DNA were strongly inhibitory to DNA polymerase β; the inhibition made the DNA useless as a template for this enzyme. In a pre-assembled DNA polymerase assay mixture (minus enzyme but including activated DNA) the inhibition tended to diminish with time but at a rate that was not predictable, and some inhibition usually persisted. It was concluded that the inhibition was the result of contamination of the DNA by a heparin-like material on the basis of the following: 1) the inhibition could be reversed by treatment of the DNA with heparinase; 2) both the endogenous inhibitory effect of calf thymus DNA as well as the inhibitory effect of heparin on DNA polymerase a are reversed by protamine (which is known to prevent the antithrombin activity of heparin); 3) both the endogenous inhibition and inhibition by heparin are also reversed by ampholyte (which also prevents the antithrombin activity of heparin); and 4) both the endogenous and the heparin-induced inhibitory effects display the same spectrum of activity against mammalian DNA polymerases, i.e. both DNA polymerases α and β are extremely sensitive whereas, DNA polymerases β and γ are resistant. The last result also suggests the use of heparin as a specific inhibitor of purified mammalian DNA polymerases α and γ, similar to the use of aphidicolin. © 1990 Oxford University Press.