Biological consequences of clustered DNA damage containing a single strand break and an AP site

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 consist of a single strand break (SSB) and an apurinic/apyrimidinic (AP) site. We found a significantly lower transformation frequency for the cluster than that for either a single SSB or a single AP site, which implies that a double strand break is formed during the processing of the cluster. Also, when the two lesions were very close to each other, almost every plasmid possessed a mutation. The major types of mutation induced by the cluster were AP:C to C:G and a 1-bp deletion at the position of the AP:C pair. These results show a clear contrast to the results from clusters comprised of base lesions. We suggest that the biological consequences of clustered DNA damage strongly depends on the type of the comprising lesions.