Figure 1. Mechanisms of DNA damage induced recombination. (A) Recombination induced by a direct DSB. (B) Recombination induced by a secondary (indirect) DSB. (C) Recombination induced by gaps or nicks. The first stage in homologous recombination is processing of the primary lesion (I). For direct DSBs (A) it is resection. Adjacent lesions on opposite strands (represented as stars) are first converted into a DSB and then resected (B). Nicks or gaps (C) may be expanded without forming a DSB. The second step (II) is strand invasion, DNA synthesis and creation of a joint molecule. The third step (III) is resolution of homologous intermediates (for simplicity only one possibility of resolution is presented).