Defective Kin28, A Subunit of Yeast Tfiih, Impairs Transcription-Coupled but Not Global Genome Nucleotide Excision Repair

The essential Saccharomyces cerevisiae KIN28 gene encodes a subunit of general transcription factor TFIIH, a multiprotein complex required for RNA polymerase II transcription initiation and nucleotide excision repair (NER). Kin28 is implicated in the transition from transcription initiation to transcription elongation by phosphorylation of the carboxy-terminal domain (CTD) of the largest subunit of the RNA polymerase II complex. Here, we explore the possibility that Kin28 like the other subunits of TFIIH is involved in NER in vivo, using yeast cells carrying either a wildtype or a thermosensitive KIN28 allele. The removal of UV induced cyclobutane pyrimidine dimers (CPDs) was monitored at base resolution from both strands of the RNA polymerase II transcribed genes RPB2 and URA3. Cells carrying the thermosensitive KIN28 allele display a transcription-coupled repair (TCR) defect at the non-permissive temperature, which was most pronounced directly downstream of transcription initiation, probably as an indirect result of a general decrease in the level of RNA polymerase II transcription. The fact that CPD removal in non-transcribed DNA is completely unaffected in these cells indicates that Kin28 is not essential for general NER in vivo, providing the first example of a TFIIH subunit that is required for TCR but not for NER in general.