摘要：Ionizing radiation and hydrogen peroxide (H 2 O 2 ) produce many types of oxidative DNA damage such as strand breaks, apurinic/apyrimidinic (AP) sites, base modifications and 3''-blocking damage such as 3''-phosphoglycolated and 3''-phosphorylated termini. AP sites and 3''-blocking damage are repairable by exonuclease III and endonuclease IV in Escherichia coli . XthA-nfo double mutants of E. coli , which are deficient in exonuclease III and endonuclease IV, were highly sensitive to lethal and mutagenic effects of H 2 O 2 , compared with the wild-type strains. The pNT180 and pNT186 plasmids containing wild-type nfo and mutant nfo-186 gene, respectively, were introduced into the xthA-nfo mutant. The nfo-186 gene product, Nfo186, retained normal AP endonuclease activity but could not remove 3''-blocking damage from DNA. The pNT180 corrected the sensitivity of the xthA-nfo mutant to lethal and mutagenic effects of H 2 O 2 . On the other hand, the pNT186 did not have any complementation effects. From these results it was concluded that 3''-blocking damage rather than an AP site is the primary lesion responsible for both lethal and mutagenic effects of H 2 O 2 .
