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 brea kage (air-saturated sample Phi(ssb) = [1.5 +/- 0.1] x 10(-4), argon-sa turated sample Phi(ssb) = [0.9 +/- 0.1] x 10(-4)). Treatment of the ir radiated DNA samples with Escherichia coli formamidopyrimidine-DNA gly cosylase (Fpg) protein results in an approximate 20-fold increase in t he yield of single strand breakage (air-saturated sample Phi(fpg) = [3 3.1 +/- 3.1] x 10(-4), argon-saturated sample Phi(fpg) = [23.8 +/- 2.6 ] x 10(-4)), This result indicates that 193 mn light induces other mod ification(s) (most likely of the purine moieties) that are 20 times mo re abundant than prompt strand breakage within the DNA matrix.