Mutant DNA polymerases
DNA binding domain
dNTP binding Domain
Springer Online Journal Archives 1860-2000
Abstract To investigate whether DNA replication in malignant cells deviates from that of normal cells we compared DNA polymerases α, δ, and ɛ from normal rat liver to the enzymes from fast-growing (malignant) Novikoff hepatoma cells. DNA polymerases were purified 300-fold by three chromatographic steps. Characterization included measurement of physicochemical constants (including sedimentation coefficients, diffusion coefficients, calculation of relative molecular masses), quantitation of catalytic activities using specific DNA primer templates (K m values) and inhibitors (K i values), and identification of polypeptides which are strongly associated with DNA polymerases. Comparison of physicochemical and catalytic properties of DNA polymerases from both sources revealed similarities but also some important differences. DNA primase associated with DNA polymerase α, and 3′–5′ exonuclease accompanying DNA polymerases δ and ɛ had similar activities. In contrast, the DNA-binding domain of DNA polymerases α and ɛ from hepatoma cells was altered since K m values, determined with the specific primer templates gapped calf thymus DNA and poly(dA·dT), were higher. Furthermore, sedimentation and diffusion coefficients, Stokes' radii, and frictional coefficient ratios of DNA polymerases α and ɛ from malignant cells significantly deviated. In addition, when the dNTP-binding sites were probed with specific inhibitors (aphidicolin, butylphenyl-dGTP, carbonyldiphosphonate, and dideoxy-TTP), significantly lower K i values were obtained for the polymerases from Novikoff cells indicating lower affinity of the dNTP binding site to deoxyribonucleoside 5′-triphosphates. Altered catalytic and molecular properties are possibly a consequence of malignant transformation. It is to be expected that similar changes occur in DNA polymerases of other tumors. In particular, diminished affinity to primer templates and weakened nucleotide binding leads to lowered specificity of nucleotide selection in the base-pairing process and is therefore likely to cause an enhanced mutation rate during malignant progression.
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