The Priming Activity of X-Irradiated Mammalian Deoxyribonucleic Acid for the Deoxyribonucleic Acid Polymerase from Calf Thymus

Abstract We have investigated the ability of calf thymus deoxyribonucleic acid, subjected to a mild x-irradiation, to prime for the partially purified deoxyribonucleic acid polymerase from the same tissue. Solutions of 50 to 400 µg per ml of DNA in 10-2 m phosphate or tris(hydroxymethyl)aminomethane buffer, pH 7.0 to 8.0, were exposed to doses up to 2000 r. This treatment had apparently no effect on the primer saturation curves obtained when increasing quantities of DNA were incubated for a standard period with substrates at optimal concentration and in the presence of a constant amount of enzyme. The results have shown that a moderate x-irradiation of isolated mammalian DNA does not cause molecular damages affecting the duplication rate of single stranded DNA chains by a base-pairing mechanism, while it is catalyzed by the DNA polymerase from calf thymus in vitro.