Post-incision events in excision repair in Escherichia coli

Long repair replication patches are produced by the short-patch pathway in a uvrD252 (recL152) mutant of Escherichia coli K-12

The uvrD252 mutation leads to increased UV sensitivity, diminished dimer excision and host cell reactivation capacity, and an increase in the average patch size after repair replication. A recA56 uvrD252 double mutant was far more resistant to UV than was a recA56 uvrB5 double mutant. Its host cell reactivation capacity was identical to that of uvrD252 single mutant and was far greater than that of the uvrB5 single mutant. The strain showed no Weigle reactivation. From these results, we concluded that the double mutant has no inducible DNA repair (including long-patch excision repair) but retains dimer excision capabilities comparable to the uvrD252 single mutant. It appears, therefore, that the long patches detected in the uvrD mutant were not identical to the recA-dependent patches seen in wild-type cells.

DNA repair synthesis in toluenized Escherichia coli treated with 8-methoxypsoralen and 365-nm light

Irradiation of permeable Escherichia coli in the presence of 8-methoxypsoralen was found to elicit DNA-repair synthesis. The incorporation depended on the uvrA+ and polA+ genes, but was unaffected by mutations at recA, B or C. Double-irradiation experiments, in which the relative influence of monoadducts and crosslinks could be measured, revealed that the repair synthesis initiated at monoadducts in the DNA. Thus these lesions appear to be subject to conventional excision repair. Crosslinks, however, blocked extensive synthesis. The significance of these results is considered in the light of recent results in vivo.