A new pathway for repair of cross-linkable 8-methoxypsoralen mono-adducts in Uvr strains of Escherichia coli.

UvrA-deficient Escherichia coli bacteria possess a DNA repair pathway for certain photoinduced mono-adducts of 8-methoxypsoralen. Such adducts can be converted to highly lethal cross-links by a second exposure to near-UV light in the absence of 8-methoxypsoralen. If a period of incubation is allowed to intervene between the primary and cross-linking exposure, the lethal effect is considerably diminished, indicating that some of the mono-adducts become unavailable for cross-linking. A repair pathway is postulated which is pre-replicative, unaffected by chloramphenicol, acriflavine or caffeine, and inhibited at 0 degrees C. It is unaffected by a rep mutation but is blocked by a polA mutation, suggesting that it involves DNA strand breakage and at least some exonuclease action.