Inhibition of DNA strand break rejoining in ultraviolet-irradiated human cells: comparison of aphidicolin and cytosine arabinoside.

When ultraviolet-irradiated mammalian cells are incubated in the presence of aphidicolin or cytosine arabinoside (ara C) DNA breaks accumulate. When the inhibitors are removed before a steady-state level of breaks has been reached, breaks accumulated in the presence of aphidicolin are rapidly sealed while breaks in ara-C-treated cells continue to increase. This suggests that the active metabolite of ara C, ara CTP, cannot, in contrast to aphidicolin, be easily washed out of cells.