What structural change in DNA is primarily repaired by nucleotide excision repair?

Nucleotide excision repair is a crucial DNA repair mechanism that primarily targets and fixes bulky DNA adducts. These adducts often arise from various forms of DNA damage, such as those caused by environmental agents like UV light or chemical mutagens, leading to the incorporation of large groups of atoms that distort the DNA helix. These alterations can disrupt normal base pairing and hinder essential cellular processes like replication and transcription.

In the nucleotide excision repair process, the damaged region of DNA is recognized, excised, and then replaced with the correct nucleotides. This repair is essential for maintaining genomic integrity and preventing mutations that could lead to diseases, including cancer. The specificity of nucleotide excision repair for bulky lesions makes it particularly important for addressing specific types of DNA damage that are not efficiently repaired by other mechanisms, such as base excision repair, which deals with smaller, non-bulky lesions.

The focus on bulky DNA adducts distinguishes this repair pathway and emphasizes its role in handling more severe forms of DNA damage compared to the other options presented, which involve different types of DNA alterations that are addressed by other repair mechanisms.