DNA synthesis and degradation in UV-irradiated toluene treated cells of E. coli K12: the role of polynucleotide ligase.

Toluene treated cells have been used to study the processes of DNA synthesis and DNA degradation in ultra-violet irradiated Escherichia coli K12. Synthesis and degradation are both shown to occur extensively if polynucleotide ligase is inhibited, and to occur to a much lesser extent if ligase activity is optimal. Extensive UV-induced DNA synthesis in toluene-treated cells requires ATP for the initial incision step, and DNA polymerase I. Extensive degradation also depends on the early ATP-dependent incision step, and the subsequent degradation shows a partial requirement for ATP. Curtailment of degradation by ligase requires DNA polymerase activity, but is not dependent upon DNA polymerase I. Apparently this process can be carried out with equal facility by either DNA polymerase II or polymerase III. These observations suggest that extensive DNA polymerase I-dependent repair synthesis and extensive DNA degradation are facets of two divergent pathways of excision repair, both of which depend upon the early uvrABC determined ATP-dependent incision step.