Thielmann H W, Hecht R
J Cancer Res Clin Oncol. 1980;96(3):243-57. doi: 10.1007/BF00408097.
Superhelical DNA of the Pseudomonas phage PM2 was irradiated with UV-light or reacted with covalently binding carcinogens, such as 7-bromomethyl-benz[a]anthracene, (Ac)2ONFln, K-region epoxides, and alkylating agents. Migration velocity of the DNA products was determined using agarose gel electrophoresis. In gels of more than 1.3%-1.9% agarose, modified PM2 DNA exhibited a dose-(concentration-)dependent decrease of migration velocity. This phenomenon is probably due to a decrease in superhelix density which caused the compact DNA coil to assume eventually an open-circular conformation. Comparison of the extent of DNA modification with the decrease of migration velocity revealed that the superhelical structure sensitively reflected the chemical DNA alterations. DNA species exhibiting, in 1.6% agarose gels, a migration velocity of up to 30% of that of control DNA showed an increase of velocity in 0.4% agarose. Therefore, in 1.3%-1.9% agarose gels, the decrease os superhelix density is accompanied by an increase of the frictional coefficient, whereas in 0.4%-0.9% agarose gels the same decrease of superhelix density apparently led to a higher degree of flexibility of the macromolecule and/or exposure of additional electric charges.
用紫外线照射假单胞菌噬菌体PM2的超螺旋DNA，或使其与共价结合致癌物反应，如7-溴甲基苯并[a]蒽、(Ac)2ONFln、K区环氧化物和烷基化剂。使用琼脂糖凝胶电泳测定DNA产物的迁移速度。在琼脂糖浓度超过1.3%-1.9%的凝胶中，修饰后的PM2 DNA迁移速度呈剂量（浓度）依赖性下降。这种现象可能是由于超螺旋密度降低，导致紧密的DNA螺旋最终呈现开环构象。将DNA修饰程度与迁移速度下降进行比较发现，超螺旋结构能灵敏地反映DNA的化学改变。在1.6%琼脂糖凝胶中迁移速度高达对照DNA 30%的DNA种类，在0.4%琼脂糖中迁移速度增加。因此，在1.3%-1.9%琼脂糖凝胶中，超螺旋密度降低伴随着摩擦系数增加，而在0.4%-0.9%琼脂糖凝胶中，相同程度的超螺旋密度降低显然导致大分子柔韧性提高和/或额外电荷暴露。
