369 Biochimica et Biophysica Acta, 561 (1979) 369--382 © Elsevier/North-Holland Biomedical Press BBA 99382 DISTINCTIVE PROPERTIES OF MAMMALIAN DNA POLYMERASES DIPAK K. DUBE *, THOMAS A. KUNKEL, GITA SEAL and LAWRENCE A. LOEB ** The Institute for Cancer Research, The Fox Chase Cancer Center, Philadelphia, PA 19111, and The Joseph Gottstein Memorial Cancer Research Laboratory, Department of Pathology, University of Washington, Seattle, WA 98195 (U.S.A.) (Received May 30th, 1978) Key words: DNA polymerase forms: (Mammalian) Summary DNA polymerase-a and -{~ can be distinguished from one another by the differential effects of N-ethylmaleimide, KC1, ara-CTP and temperature, as well as on the basis of sedimentation. The sensitivity of DNA polymerase-~ to elevated temperatures as compared to DNA polymerase-a provides a new means of distinguishing between these two enzymes even in crude extracts and a possible probe for determining their function. DNA polymerase-a and -fl share several properties in common, including the ability to readily incorporate dUTP in place of dTTP. The K m for dUTP varies from 10 to 30 pM with different preparations of DNA polymerase-a and -{]. Thus, in mammalian cells, dUMP could be incorporated into DNA, and if excised by an endonuclease, would lead to discontinuities. Initial analyses of fidelity in direct comparative studies indicate that/3-class DNA polymerases are highly accurate in base selection when copying poly[d(A-T)]. Less than one molecule of dGMP is incorporated for every 12 000--45 000 molecules of dAMP and dTMP polymerized. DNA polymerase-a is somewhat less accurate, making one mistake for every 4000--10 000 correct nucleotides incorporated. Since both polymerases lack an exonucleolytic activity, this accuracy must be the result of selectivity for the complementary nucleotide by the polymerase. Introduction Multiple species of DNA polymerases have been isolated from a variety of eukaryotic cells [1--3]. In mammalian cells these are referred to as DNA polymerase~, 9,-7 and mitochondrial (mt) DNA. Recent evidence suggests that * Permanent address: Department of Biochemistry, Calcutta University, Calcutta, 700 019, India. ** To whom reprint requests should be addressed at the Joseph Gottstein Memorial Cancer Rese~Lrch Laboratory.