¹Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanita', Viale Regina Elena 299, 00161 Rome, Italy

²Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, UK

³UMR 1772 CNRS, Groupe Reparation de l'ADN, Institut Gustave Roussy, 39 Rue C. Desmulins, Villejuif Cedex 94805, France

Correspondence to: E Dogliotti, E-mail: dogliott@iss.it

Replication of DNA containing 8-oxo-7,8-dihydroguanine (8oxoG) can generate 8oxoG/A base pairs which, if uncorrected, lead to GT transversions. It is generally accepted that the repair of these promutagenic base pairs in human cells is initiated by the MutY DNA glycosylase homolog (hMYH). Here we provide biochemical evidence that human cell extracts perform base excision repair (BER) on both DNA strands of an 8oxoG/A mismatch. At early repair times the specificity of nucleotide incorporation indicates a preferential insertion of C opposite 8oxoG leading to the formation of 8oxoG/C pairs. This is followed by repair synthesis on the opposite DNA strand that is consistent with hOGG1-mediated correction of 8oxoG/C to G/C. Repair synthesis on either strand is completely inhibited by aphidicolin suggesting that a replicative DNA polymerase is involved in the gap filling. This is the first demonstration that repair of 8oxoG/A base pairs is by two BER events likely mediated by Pol/. We suggest that the Pol/-mediated BER is the general mode of repair when BER lesions are formed at replication forks.

Oncogene (2002) 21, 5204-5212. doi:10.1038/sj.onc.1205561

DNA repair; oxidative damage; mammalian cell extracts; base excision repair; 8oxo G/A mismatch