Characterization of clustered DNA damage-induced mutations in

Shikazono, Naoya; Noguchi, Miho; Urushibara, Ayumi; O'Neill, P.*; Yokoya, Akinari

Using a bacterial plasmid-based assay, we have investigated the biological consequences of bistranded clustered damage sites which are comprised of combinations of base lesions, AP sites, and SSBs. Plamids were ligated with oligonucleotides with clustered lesions. Following transformation of the ligated plasmids into wild type strain of Escherichia coli, clustered damage-induced mutations were characterized. Although the transformation efficiencies were low, the major types of mutation induced by the AP + AP or AP + SSB cluster were G insertion opposite AP and a 1-bp deletion at the base pair with AP. On the other hand, mutations were occasionally found at base pairs where lesions had not been placed with clusters such as DHT + 8-oxoG, and DHT + SSB. From these results, we suggest that, in a bistranded base cluster, (1) either base lesion is remained unrepaired and (2) some mutations arise not at but very close to the base pair where base lesions were originally placed.