Factors affecting the primer for deoxyribonucleic acid polymerase

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Abstract
Experiments have been carried out to assess the priming ability of some deoxyribonucleic acid preparations in the deoxyribonucleic acid-polymerase system from Landschutz ascites-tumour cells. Thermally denatured deoxyribonucleic acid from Landschutz ascites-tumour cells had a priming capacity 7 times that of native deoxyribonucleic acid. Prolonged thermal treatment, however, reduced the priming capacity. The single-stranded deoxyribonucleic acid from bacteriophage OX 174 was greatly superior to thermally denatured Landschutz-tumour deoxyribonucleic acid in priming capacity. Limited treatment of Landschutz-tumour deoxyribonucleic acid with pancreatic deoxyribonuclease improved its priming capacity by about 60%, but subsequent thermal denaturation gave a primer 11 times as efficient as the native deoxyribonucleic acid. Solutions of Landschutz-tumour deoxyribonucleic acid in 0.01 M buffer, pH 8 or pH 9, were capable of priming the polymerase reaction at pH 7.5 efficiently before as well as after thermal treatment. When the solution was prepared in 0.01 M buffer, pH 7, thermal treatment was required to produce an active primer. Thermal denaturation of deoxyribonucleic acid from Landschutz-tumour cells was accompanied by a hyperchromic effect at 260 m[mu], the magnitude of which was dependent upon the salt concentration of the medium. Hyperchromicity after thermal treatment was also displayed by the deoxyribonucleic acid solutions in 0.01 M buffer, pH 8 and pH 9. Attempts to demonstrate a return of thermally denatured deoxyribonucleic acid to the native state by slowly cooling the heated solution in 0.15 M-sodium chloride-0.015 M-sodium citrate indicated that there was no reversal of denaturation as revealed by measurements of priming capacity and extinction. A preparation of deoxyribonucleic acid from bacteriophage T2, although exhibiting hyperchromicity after thermal treatment, was capable of priming the poly-merase reaction before as well as after heating, and to the same extent.

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