Which DNA Repair Mechanism Involves Recombination?

DNA damage can arise from various sources such as UV radiation, chemical mutagens, and replication errors. Cells have evolved multiple repair mechanisms to maintain genomic integrity. Among these, some repair pathways involve recombination—a process where DNA strands are exchanged to repair breaks or lesions. Understanding which repair mechanisms utilize recombination is essential for comprehending cellular responses to DNA damage.

Overview of the Repair Mechanisms Listed

1. Photoactive Direct Repair Mechanism:

   • This repair directly reverses DNA damage, such as pyrimidine dimers caused by UV light, using photolyase enzymes activated by visible light.

   • It does not involve recombination.

2. SOS Repair Mechanism:

   • The SOS response is a global bacterial response to extensive DNA damage.

   • It induces expression of multiple genes, including those involved in DNA repair, replication, and recombination.

   • Recombination repair is a key component of the SOS response, especially for repairing double-strand breaks and stalled replication forks.

   • RecA protein plays a central role in mediating homologous recombination during SOS repair.

3. Post-Replication Repair Mechanism:

   • This pathway allows cells to bypass lesions during DNA replication and later repair the damage.

   • It often involves recombination-based processes to restore the correct DNA sequence.

4. Nucleotide Excision Repair Mechanism:

   • This pathway removes bulky DNA lesions by excising a short single-stranded DNA segment containing the damage, followed by repair synthesis.

   • It is a cut-and-patch mechanism and does not involve recombination.

Evidence from Scientific Literature

• The SOS response activates recombination repair proteins such as RecA, RuvAB, and RecN to process DNA double-strand breaks and gaps.

• Studies show that recombination repair is essential during the SOS response to maintain genome stability under stress.

• Post-replication repair also utilizes recombination to bypass lesions and restore DNA integrity.

• Photoreactivation and nucleotide excision repair operate independently of recombination.

Correct Answer

(2) SOS repair mechanism

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Conclusion

Among the listed DNA repair mechanisms, only the SOS repair mechanism involves recombination. This pathway is activated in response to severe DNA damage and utilizes homologous recombination proteins to repair double-strand breaks and stalled replication forks. Other mechanisms like photoactive direct repair and nucleotide excision repair do not involve recombination.

Correct answer: (2) SOS repair mechanism