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Characteristics of Deoxyribonucleic Acid Polymerase Isolated from Spores of Rhizopus stolonifer¹

^a Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska 68503

ABSTRACT

Deoxyribonucleic acid (DNA)-dependent DNA polymerase was purified several hundredfold from germinated and ungerminated spores of the fungus Rhizopus stolonifer. The partially purified enzymes from both spore stages exhibited identical characteristics; incorporation of [³H]deoxythymidine monophosphate into DNA required Mg²⁺, DNA, a reducing agent, and the simultaneous presence of deoxyguanosine triphosphate, deoxycytidine triphosphate, and deoxyadenosine triphosphate. Heat-denatured and activated DNAs were better templates than were native DNAs. The buoyant density of the radioactive product of the reaction was similar to that of the template DNA. The enzyme is probably composed of a single polypeptide chain with an S value of 5.12 and an estimated molecular weight of 70,000 to 75,000. During the early stages of purification, the enzyme fraction from ungerminated spores required exogenous DNA for maximum activity, whereas the corresponding enzyme fraction from germinated spores did not require added DNA. Apparently DNA polymerase from germinated spores was more tightly bound to endogenous DNA than was the enzyme from ungerminated spores.

¹ Published as paper no. 3553, Journal Series, Nebraska Agricultural Experiment Station. Research reported was conducted under project no. 21-17.