Which type of DNA repair is responsible for fixing double-strand breaks?

Double-strand breaks in DNA are particularly severe forms of damage that can lead to genomic instability if left unrepaired. The type of DNA repair specifically designated for addressing these breaks is known as double-strand break repair. This process primarily includes two mechanisms: homologous recombination (HR) and non-homologous end joining (NHEJ).

Homologous recombination uses a sister chromatid as a template, allowing for precise repair, particularly important during the S and G2 phases of the cell cycle when sister chromatids are available. Non-homologous end joining, on the other hand, is a quicker repair mechanism that directly joins the broken ends without a need for a homologous template, which is critical in the G1 phase when sister chromatids are not present.

Other types of DNA repair are tailored to different types of damage. For instance, base excision repair specifically addresses non-helix-distorting base lesions, while nucleotide excision repair is meant for bulky DNA adducts and helix-distorting lesions. Direct repair mechanisms fix specific types of damage directly without needing excision or synthesis.

Thus, recognizing that double-strand break repair is uniquely structured to manage the complexities of repairing double-strand breaks underscores why this