DNA interstrand cross-links induce futile repair synthesis in mammalian cell extracts

DNA interstrand cross-links are induced by many carcinogens and anticancer drugs. It was previously shown that mammalian DNA excision repair nuclease makes dual incisions 5' to the cross-linked base of a psoralen cross-link, generating a gap of 22 to 28 nucleotides adjacent to the cross-link, We wis hed to find the fates of the gap and the cross-link in this complex structu re under conditions conducive to repair synthesis, using cell extracts from wild-type and cross-linker-sensitive mutant cell lines. me found that the extracts from both types of strains filled in the gap but were severely def ective in ligating the resulting nick and incapable of removing the cross-l ink. The net result was a futile damage-induced DNA synthesis which convert ed a gap into a nick without removing the damage. In addition, in this stud y, we showed that the structure-specific endonuclease, the XPF-ERCC1 hetero dimer, acted as a 3'-to-5' exonuclease on cross-linked DNA in the presence of RPA Collectively, these observations shed some light on the cellular pro cessing of DNA cross-links and reveal that cross-links induce a futile DNA synthesis cycle that mag constitute a signal for specific cellular response s to cross-linked DNA.