Fig. 4.

Schematic representation of repair of dL/8-oxodGuo clusters in E. coli. The two lesions within the cluster are repaired sequentially, thus avoiding the formation of a DSB. First the dL lesion is repaired by long patch BER, incorporating thymine and cytosine in to the repair patch (1). Then 8-oxodGuo (Go) is repaired (2), resulting in correct repair of the clustered DNA damaged site with no formation of mutations (A). As the lifetime of the lesions within the cluster is extended, replication could occur before repair takes place (3). 8-oxodGuo (Go) can exist in two forms and can base pair with cytosine (4) or adenine (5). Base pairing with cytosine results in non-mutagenic repair of the clustered DNA damaged site (A). An incorrectly base paired adenine can be removed by mutY, allowing correct base pairing to take place (6). If the incorrectly base paired adenine is not removed then repair of 8-oxodGuo (Go) results in a G:C to T:A transversion (C). The existence of other mutations in addition to G:C to T:A transversions demonstrates that retarded LP-BER of dL could lead to small deletions (C).