Which repair pathways correspond to the following damages: mispaired bases, damaged or modified bases, and bulky lesions/UV-induced dimers, respectively?

• A. Mismatch repair; base-excision repair; nucleotide-excision repair.
• B. Mismatch repair; nucleotide-excision repair; base-excision repair.
• C. Base-excision repair; mismatch repair; nucleotide-excision repair.
• D. Nucleotide-excision repair; mismatch repair; base-excision repair.

Answer: (A)

Different DNA repair pathways specialize for different damages. Mispaired bases arise from replication errors, and mismatch repair specifically recognizes and corrects these mispairs by removing a short DNA segment containing the error and resynthesizing it. Damaged or modified bases, such as oxidized or deaminated bases, are handled by base-excision repair, where a DNA glycosylase removes the damaged base, creating an abasic site that is then processed and filled in. Bulky lesions and UV-induced dimers distort the DNA helix and are efficiently removed by nucleotide-excision repair, which excises a stretch of DNA containing the lesion and replaces it with the correct sequence. Putting these together, the correct mapping is mispaired bases with mismatch repair, damaged or modified bases with base-excision repair, and bulky lesions/UV-induced dimers with nucleotide-excision repair.