To prevent such catastrophic events, cells have evolved intricate mechanisms to repair DNA double-strand breaks. These mechanisms include two main pathways: homologous recombination (HR) and non-homologous end-joining (NHEJ).
Homologous recombination utilizes a homologous DNA sequence as a template to repair the broken DNA. This pathway is highly accurate and primarily occurs during the S and G2 phases of the cell cycle when a sister chromatid is available as a template.
Non-homologous end-joining, on the other hand, directly ligates the broken DNA ends without the need for a template. While faster and less dependent on the cell cycle stage, this pathway is more prone to errors and may result in small insertions or deletions at the repair site.
The choice between HR and NHEJ is influenced by several factors, including the availability of a homologous template and the cell cycle stage. In general, HR is preferred when a homologous sequence is present and the cell is in the S or G2 phase. In contrast, NHEJ is more frequently employed when there is no available template or in rapidly dividing cells where HR is less efficient.
It is worth noting that beyond these two main pathways, other mechanisms can contribute to the repair of DNA double-strand breaks, including alternative end-joining and single-strand annealing.
Understanding the mechanisms employed by cells to repair DNA double-strand breaks is of paramount importance in various fields, ranging from cancer research to radiation therapy. By targeting these mechanisms, novel therapeutic approaches can be developed to selectively kill cancer cells while sparing healthy tissues.
