CPD-seq mapping of transcription-coupled DNA repair in yeast

Transcription-coupled nucleotide excision repair (TC-NER) is an important DNA repair mechanism that responds to RNA polymerase (RNAP) stalling and removes DNA lesions from transcribed genes. Activation of TC-NER requires specific factors, such as human Cockayne syndrome group B (CSB) protein or its yeast homolog Rad26. Mutations in CSB are associated with the severe neurological disorder Cockayne syndrome. However, the genome-wide role of CSB/Rad26 in TC-NER, particularly in the context of chromatin organization, is not fully understood. Here we used single-nucleotide resolution UV damage mapping data to investigate the genome-wide function of Rad26 in TC-NER. Our data shows that Rad26 is critical for TC-NER in transcribed regions downstream of the first (+1) nucleosome; however, Rad26 is largely dispensable for TC-NER in the +1 nucleosome. We further show that the Rad26-independent TC-NER in the +1 nucleosome is correlated with high occupancy of the transcription initiation/repair factor TFIIH. Downstream of the +1 nucleosome, the combination of low TFIIH occupancy and high occupancy of the transcription elongation factor Spt4/Spt5 suppresses TC-NER when Rad26 is dysfunctional. Deletion of SPT4 significantly restores TC-NER in the downstream nucleosomes in a rad26∆ mutant. Collectively, these data indicate that the requirement for Rad26 in TC-NER is modulated by the distribution of TFIIH and Spt4/Spt5, and Rad26 mainly functions in the downstream nucleosomes to remove TC-NER suppression by Spt4/Spt5. UV-induced CPD lesions are mapped using a high throughput method named CPD-seq. CPD-seq data generated in WT, RAD26 deletion, and Rad26 ATPase-dead yeast strains were analyzed to study the genome-wide role of Rad26 in TC-NER.