DNA repair pathway in alkylated human cells: apurinic/apyrimidinic intermediate resolved by Escherichia coli endonuclease IV-coupled alkaline elution

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Abstract
Apurinic/apyrimidinic (AP) sites were measured in HeLa cells by digestion of cellular DNA with Escherichia coli endo-nuclease IV, an AP-specific endonuclease, prior to alkaline elution. The absence of non-specific endonuclease activity allowed endonuclease IV-sensitive AP sites to be detected with the sensitivity of conventional alkaline elution. Cells that were alkylated with dimethyl sulfate contained AP sites that were repaired along with DNA single-strand breaks during a post-alkylation recovery period. These results show that DNA alkylation products are repaired, at least in part, via an AP intermediate suggesting a repair pathway initiated by DNA glycosylases followed by DNA incision by AP endonuclease.