Inhibition of repair of DNA single strand breaks in mouse leukemia cells by actinomycin D

The effects of Actinomycin D, cytosine arabinoside and temperature shifts on the repair of single strand breaks produced in murine leukemia cell DNA by ionizing radiation have been studied. A recently introduced modification of the alkaline sucrose sedimentation methods was used, allowing breaks to be demonstrated following clinical range irradiation doses. The results contrast to previous data using standard gradient procedures and indicate that low concentrations of Actinomycin D can inhibit single strand break repair, while cytosine arabinoside is ineffective. Inhibition can also be demonstrated by temperature shifts to 3° but not 24°, paralleling previous results from cellular repair studies (Elkind-Sutton repair). The results are consistent with the hypothesis that the accumulation of sublethal radiation damage in mammalian cells may be based on residual non-repaired single strand breaks.