Studies on Escherichia coli X-Ray Endonuclease Specificity: Roles of Hydroxyl and Reducing Radicals in the Production of DNA Lesions

Abstract

DNA strand breakage induced by X irradiation, by X irradiation and alkali treatment, or by X irradiation and subsequent incubation with E. coli X-ray endonuclease was measured by the conversion of PM2 Type I DNA to Type II. The hydroxyl radical mediated the formation of alkali-labile lesions and to a lesser extent simple strand breaks. All alkali-labile lesions were also enzyme-sensitive sites. When the effective concentration of hydroxyl radicals was reduced by radical scavenging, reducing species appeared to produce enzyme sensitive sites which were not alkali labile. Tryptone-glucose-yeast extract medium, which was used in an attempt to simulate cellular conditions, protected against strand breakage, alkali-labile lesions and non-alkali-labile enzyme-sensitive damages. The E. coli X-ray endonuclease recognized OsO4 induced DNA damages which are identical to the radiolysis products of thymine produced by ionizing radiation.