Excision repair participates in the Weigle reactivation of ultraviolet light-irradiated phi X174 double-stranded DNA

The efficiency of Weigle reactivation of ultraviolet light-irradiated single and double-stranded phi X174 DNA by wild-type and excision repair-defective E. coli hosts was determined. After limited exposure to ultraviolet light, the efficiency of Weigle reactivation by an ultraviolet light-irradiated wild-type host was greater for double-stranded phi X174 DNA than for its single-stranded counterpart. However, the efficiency of inducible recovery of the double-stranded DNA molecule decreased as its exposure to ultraviolet light increased until it became constant at a value 1.5 times less than that for single-stranded form of phi X174 DNA. The efficiency of Weigle reactivation of the single-stranded DNA molecule by the same host, however, was independent of the dose to the DNA, as were the efficiencies of reactivation for both forms of phi X174 DNA by ultraviolet light-irradiated excision repair-deficient hosts. In excision repair-defective hosts the efficiency of Weigle reactivation of double-stranded phi X174 DNA was also 1.5 times less than that for the single-stranded molecule. These results suggest that the Weigle reactivation of double-stranded phi X174 DNA is mediated in part by an excision repair process, and that this component of Weigle reactivation eventually can be saturated by ultraviolet light-induced DNA damage leaving other repair processes, such as trans-damage synthesis, responsible for the remaining inducible reactivation.