Effects of vacuum UV and UVC radiation on dry E. coli plasmid pUC19. I. Inactivation, lacZ- mutation induction and strand breaks.

Using Escherichia coli plasmid pUC19 as a test system to study the effects of radiation on DNA at the molecular level, the wavelength (160-254 nm) dependence of inactivation (loss of the ability to transform E. coli), mutation induction in the target gene lacZ and induction of single-strand breaks and double-strand breaks was investigated. The same fluences were applied for all endpoints tested. In the UVC range, the cross-sections of inactivation and mutation induction match the DNA absorption curve, whereas the cross-section for single-strand break induction deviates from the DNA curve, especially at 220 nm. In the vacuum UV range, with increasing energy of the photons, the cross-sections of inactivation and single-strand breaks increase sharply (from 190 to 160 nm by more than one order of magnitude), which is not reflected by the DNA curve. In this UV range, the shape of the action spectrum is similar to that of the absorption curve of the sugar phosphate moiety of DNA. Only after irradiation with vacuum UV at 160 nm are double-strand breaks detected. Their induction rate is about one order of magnitude lower than that of single-strand breaks at the same wavelength; however, their induction rate is at least twice that of single-strand breaks at longer wavelengths. Concerning mutation induction, the increment in the vacuum UV range is less well expressed. The data suggest the contribution of different kinds of photochemical injury to inactivation and mutation induction.