Final answer:
Cockayne syndrome patients are deficient in the transcription-coupled pathway of nucleotide excision repair, which specifically targets DNA lesions that obstruct transcription and is crucial for resolving damage-induced transcriptional stalling.
Step-by-step explanation:
The DNA repair mechanism that is deficient in cells from a Cockayne syndrome patient is the transcription-coupled pathway of nucleotide excision repair. This pathway is specifically responsible for removing the DNA damage that actively blocks transcription.
Cockayne syndrome (CS) is a rare genetic disorder characterized by sensitivity to sunlight, severe neurological abnormalities, and premature aging. Patients with CS exhibit a specific deficiency in the transcription-coupled repair (TCR) pathway of nucleotide excision repair (NER). This pathway is pivotal in rapidly removing DNA lesions from the template strand that is being transcribed into RNA.
The NER mechanism has two sub-pathways: the global genome NER (GG-NER) and the transcription-coupled NER (TC-NER). While GG-NER patrols the entire genome for damage, the TC-NER pathway is more targeted, dealing with damage that blocks transcription machinery. The latter pathway is defective in individuals with Cockayne syndrome, leading to the accumulation of DNA damage and contributing to the symptoms of the syndrome.