Saturation of dark repair synthesis: accumulation of strand breaks.

Reversal of ultraviolet light damage to DNA by the dark repair system is limited. Experiments utilizing density and radioactive labels demonstrated that repair synthesis is not proportional to dose at doses above 200 ergs/mm(2). In addition, the number of residual excision induced gaps in Escherichia coli B/r hcr(+) DNA increases with higher UV doses. The extent of repair is apparently limited by saturation of the repair synthesis step.