Studies on Agrobacterium tumefaciens VI. α-DNA polymerases of crown-gall tumor and normal cells, and of the bacterium

Abstract

No consistent differences were found in the specific activities of DNA polymerase-α in normal and crown-gall tumor cell lines of both Vinca rosea and Nicotiana tabacum, suggesting that abnormally high DNA polymerase activity is not necessarily associated with the transformed state per se. No major differences in template preferences were observed between the enzymes of normal and tumor cell lines, both of which prefer denatured DNA as template. Only the 6 S DNA polymerase (α-enzyme) with a molecular weight of 110 000 could be isolated from tumor and normal cell lines; β-polymerase (nuclear, 3·5 S) and deoxynucleotidyl terminal transferase were not detected. The misincorporation frequency of the purified 6 S polymerase from V. rosea tumors was less than 2 × 10−4 incorrect nucleotide per mole dTTP incorporated using the copolymer poly (dA–dT)n. (dA–dT)n as template, approximately the same level of incorporation found for polymerase from the normal cell line. RNA-dependent DNA polymerase (reverse transcriptase) activity was not detected in tissue extracts and in fractions separated by column chromatography. Partially purified 6·5 S bacterial DNA polymerase (mol. wt = 150 000) prefers both denatured and activated DNA over native DNA as template and no reverse transcriptase activity is associated with it.