Irradiation of DNA with 193 nm light yields formamidopyrimidine-DNA glycosylase(Fpg) protein-sensitive lesions.

Irradiation of aqueous solutions of plasmid DNA (pUC18) at pH 7.6 with 193 nm laser light results in low yields of prompt single strand breakage (air-saturated sample phi ssh = [1.5 +/- 0.1] x 10(4), argon-saturated sample phi ssh = [0.9 +/- 0.1] x 10(4). Treatment of the irradiated DNA samples with Escherichia coli formamidopyrimidine-DNA glycosylase (Fpg) protein results in an approximate 20-fold increase in the yield of single strand break-age (air-saturated sample phi fpg = [33.1 +/- 3.1] x 10(-4), argon-saturated sample phi fpg = [23.8 +/- 2.6] x 10(-4). This result indicates that 193 nm light induces other modification(s) (most likely of the purine moieties) that are 20 times more abundant than prompt strand breakage within the DNA matrix.