Co-ordination of DNA single strand break repair.

DNA damaging agents generated as a consequence of endogenous metabolism or via exogenous factors can produce a wide variety of lesions in DNA. These include base damage, sites of base loss (abasic sites) and single strand breaks (SSBs). Moreover, reactive oxygen species (ROS) create more diversity by generating SSBs containing modified 3'-ends, such as those containing phosphate, phosphoglycolate and oxidative base damage. Ionising radiation also generates DNA base lesions in close proximity to SSBs. The majority of these non-bulky lesions in DNA are repaired by proteins involved in the base excision repair (BER) pathway. It is apparent that due to the complexity of these lesions, they may require individual subsets of BER proteins for repair. However, the mechanism unravelling the required enzymes and directing damage-specific repair of SSBs is unclear. In this review we will discuss recent studies that identify new enzymes and activities involved in the repair of SSBs containing modified ends and in particular outline the possible mechanisms involved in the co-ordinated repair of "damaged" SSBs that can not be resealed directly and require preliminary processing.