The effects of nalidixic acid on X-ray-induced DNA degradation and repair in Micrococcus radiodurans

Abstract

In Micrococcus radiodurans normal DNA synthesis has two components of which one is highly sensitive to nalidixic acid (NA) and the other quite resistant. Irradiated cells repair the X-ray-induced breaks in DNA in the presence of NA except at high concentrations at which repair is inhibited through an abscopal effect of the drug on protein synthesis. Irradiated cells are stimulated to degrade a larger fraction of their DNA in the presence of moderate doses of NA even though the X-ray-induced breaks have been repaired. This effect is similar to that of phenethyl alcohol in that the normal response to the drug is not restored by DNA repair. There must, therefore, be critical X-ray-induced damage in a non-DNA target which is not repaired unless normal growth and division are resumed.