Figure 1. DNA repair and damage-monitoring pathways. The presence of DNA damage in the genome of a cell is monitored by DNA-damage sensors which, in turn, send appropriate signals to the cellular response machinery including DNA-repair pathways and cell cycle checkpoint control systems (other responses). DNA repair is thought be conducted in transcribed (gene expression) regions by the transcription-coupled repair (TCR) system or in other genomic regions by the global genome repair (GGR) system. Components of specific DNA-repair pathways that may participate in TCR or GGR are base excision repair (BER), nucleotide excision repair (NER) and mismatch repair (MMR). In some cases, DNA damage is handled by damage-tolerance pathways such as translesion synthesis (TLS) and recombination (REC).

Figure 2. Biological endpoints of unrepaired DNA damage. The consequences of inability to mount an appropriate response to the presence of DNA damage leads to a number of potentially deleterious consequences.