Degradation of nucleic acids with ozone. VI. Labilization of the double-helical structure of calf thymus deoxyribonucleic acid.

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Abstract
The degradation of calf thymus DNA (0.54 mg/ml) with ozone-containing oxygen as (ozone content, 0.1 mg/l; flow rate, 70 ml/min) was examined. The degradation rates of the 4 nucleotides in native and heat-denatured DNA were in the following order: dGMP .simeq. dTMP > dCMP .simeq. dAMP and dTMP > dGMP > dCMP .simeq. dAMP, respectively. In the case of heat-denatured DNA, the rapid degradation of the thymine moiety seems to be due to its relatively weak stacking ability, so that it is more exposed to attack. In intact DNA, the double-helical structure of DNA tends to protect the base moieties from attack by ozone. At the early stage of ozonization of native DNA, strand scission did not occur but the degradation of several guanine and/or thymine moieties was detected. As the ozonization proceeded, strand scissions of DNA and susceptibility to nuclease S1 digestion were observed. Therefore a specific ozone-denaturation or labilization occurred, causing the double-helical structure to become increasingly loose due to the destruction of guanine and/or thymine moieties, and making the structure more accessible to nuclease S1. [There has been increasing interest in the use of ozone in drinking water and waste water treatment because of its superior oxidation and sterilization power. For improving the safety margin of safety cabinets and/or safety rooms, especially those used in recombinant DNA experiments, ozone may be used.].