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DNA Polymerase -Primase Complexes from Carcinogen-treated Chinese Hamster Ovary Cells¹

German Cancer Research Center, Institute of Biochemistry, Im Neuenheimer Feld 280, 6900 Heidelberg, Federal Republic of Germany [A. B., H. W. T.], and The Joseph Gottstein Memorial Cancer Research Laboratory, Department of Pathology SM-30, University of Washington, Seattle, Washington 98195 [L. A. L.]

In order to investigate whether carcinogens induce alterations of the DNA polymerase -primase complex we compared the physicochemical and catalytic properties and the fidelity of DNA synthesis of DNA polymerase -primase complexes from carcinogen-treated and untreated Chinese hamster ovary cells. Complexes were purified by ion exchange or by immunoaffinity chromatography and both DNA-polymerizing activities and those of ancillary enzymes, such as RNA primase and exonuclease, were examined. Further characterization of the complexes included determination of the relative molecular masses, sedimentation coefficients, and diffusion coefficients, and measurements of the K_ms for deoxynucleotide triphosphates and DNA templates, which were identical for the preparations from both carcinogen-treated and untreated cells. The fidelity of DNA polymerase -primase complexes measured by the X174am3 reversion assay was also similar in carcinogen-treated and untreated cells. Thus, a carcinogen-mediated induction of a DNA polymerase -primase complex with low fidelity was not observed within the detection limits of the X174 assay.

RNA primase was found to be an ancillary enzyme activity of the DNA polymerase from both carcinogen-treated and untreated cells; however, the RNA primase:DNA polymerase activity ratio was significantly higher in DNA polymerase -primase complexes from carcinogen-treated cells. These complexes also exhibited an at least 3 times greater velocity of synthesis with supercoiled or unprimed single-stranded DNAs as templates. Since the binding sites of DNA polymerase -primase complexes for deoxynucleotide triphosphates and DNA templates were shown to be identical before and after treatment of cells with carcinogens (i.e., identical K_m values for different DNA templates and K_i values for specific inhibitors), the increased synthesis catalyzed by the DNA polymerase -primase complex from carcinogen-treated cells might be due to a carcinogen-induced alteration of an accessory protein of the complex.

¹ This research was supported in part by an International Cancer Research Technology Transfer (ICRETT) grant of the International Union Against Cancer (UICC), Geneva, to A. B., and by NIH Grant R35-CA39903 to L. A. L.

² To whom requests for reprints should be addressed.

Received 4/ 3/90. Accepted 7/13/90.

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