ENZYMATIC RECOGNITION AND BIOLOGICAL EFFECTS OF PHOTODYNAMIC DAMAGE-INDUCED IN DNA BY 1,6-DIOXAPYRENE PLUS UVA

The specific recognition of DNA modifications by repair endonucleases was used to characterize DNA damage induced by 1,6-dioxapyrene (1,6-DP ) in the presence of ultraviolet light at 365 nm (WA) in the plasmid Y Eplac181. Under cell free conditions, 1,6-DP plus WA generated lesions are recognized by the UvrABC endonuclease, the proteins Nth, Nfo and Fpg. The number of UvrABC sensitive sites was at least ten-fold higher than that of Fpg or Nth sensitive sites. Moreover, 1,6-DP plus UVA ge nerated single-strand breaks which are the second most frequent lesion s. To investigate the biological effect of DNA damage, YEplac 181 DNA was treated with 1,6-DP plus UVA and transformed into Escherichia coli or Saccharomyces cerevisiae. In Escherichia coli, the transformation efficiency of 1.6-DP plus UVA treated DNA was greatly reduced in the u vr A mutant compared to that in the wild-type strain. However, the tra nsforming efficiency was not affected in Fpg-deficient strains. In Sac charomyces cerevisiae, the transformation efficiency of 1,6-DP plus UV A treated YEplac181 was greatly reduced in the rad14::URA3 strain. The photobiological effect of 1.6-DP plus UVA was also analysed in haploi d yeast strains of various repair capacities. The results show that th e yeast strain defective in the nucleotide excision repair pathway (ra d14::URA3) is hypersensitive to 1,6-DP plus UVA treatment as compared to the parental wild-type strain. It is confirmed that the lethal effe ct of 1,6-DP plus UVA on wildtype yeast is strongly oxygen dependent, whereas the survival of the rad14::URA3 mutant only exhibits a minor o xygen dependence, To conclude, our data show that the photodynamic DNA lesions induced by 1,6-DP plus UVA can be recognized and repaired in pro-and eukaryotic cells by the nucleotide excision repair pathway. (C ) 1997 Elsevier Science S.A.