Degradation of Nucleic Acids with Ozone. VI. Labilization of the Double-Helical Structure of Calf Thymus Deoxyribonucleic Acid

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The degradation of calf thymus deoxyribonucleic acid (DNA) (0.54mg/ml) with ozonecontaining oxygen gas (ozone content, 0.1mg/l ; flow rate, 70ml/min) was examined. The degradation rates of the four nucleotides in native and heat-denatured DNAs were in the following order : dGMP≃dTMP>dCMP≃dAMP and dTMP>dGMP>dCMP≃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 S_1 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 S_1.
1984-09-25