Non-homologous end joining (NHEJ): This is the most common pathway for repairing double-strand breaks. NHEJ involves joining the broken ends of the DNA without using a template, and it is often associated with deletions or insertions at the repair site.
Homologous recombination (HR): This pathway uses a homologous region of DNA, usually from a sister chromatid, as a template to repair the broken chromosome. HR is more accurate than NHEJ and results in fewer mutations.
Single-strand annealing (SSA): This pathway occurs when two broken ends of DNA have complementary single-stranded overhangs. The overhangs can anneal to each other, allowing the broken ends to be joined together. SSA often results in deletions at the repair site.
Break-induced replication (BIR): This pathway involves replication of the damaged DNA region using a template from the opposite strand of the same chromosome. BIR is similar to HR, but it does not require a sister chromatid as a template.
Microhomology-mediated end joining (MMEJ): This pathway is similar to NHEJ, but it uses short regions of microhomology (1-20 nucleotides) as a template to join the broken ends of DNA. MMEJ is often associated with translocations and other rearrangements.
The choice of repair pathway depends on the type of DNA damage, the cell cycle stage, and the availability of a homologous template. Cells have complex mechanisms to ensure that DNA damage is repaired accurately and efficiently, minimizing the risk of mutations and genomic instability.
