Thymidine dimers must be repaired by which process?

Thymidine dimers are formed when two adjacent thymine bases in DNA become covalently linked due to ultraviolet (UV) light exposure. This aberration distorts the DNA helix and can impede DNA replication if left unrepaired. The repair process that specifically addresses these types of lesions is nucleotide excision repair (NER).

In nucleotide excision repair, the damaged section of DNA is recognized, and a segment of the strand containing the thymine dimer is excised. Subsequently, DNA polymerase synthesizes a new segment of DNA to fill in the gap, and DNA ligase seals the final product, restoring the DNA to a functional state. This mechanism is critical not only for removing thymine dimers but also for other bulky DNA adducts and various types of oxidative damage.

Other types of repair mechanisms are not equipped to handle thymidine dimers effectively. For instance, base excision repair specifically addresses single-base modifications and does not repair larger structural distortions. DNA replication is a process of copying DNA and not involved in the actual repair of lesions. Mismatch repair focuses on correcting errors that arise during DNA replication, such as non-complementary base pairing, and does not target covalent modifications like thymidine dimers. Therefore