Effect of novobiocin on degradation and repair of the superhelical structure of nuclear DNA from rat thymocyte fractions

A study was made of the action of novobiocin on degradation and repair events in supercoiled nuclear DNA from three thymocyte fractions obtained by ficoll-paque gradient sedimentation. When added before gamma-irradiation novobiocin (1.9 mg/ml) exerted a radioprotective effect during the "second wave" of supercoiled DNA degradation. It is suggested that this effect may be due to the inhibition of DNA topoisomerase II.