Excision repair at the level of the nucleotide in the upstream control region, the coding sequence and in the region where transcription terminates of the Saccharomyces cerevisiae MFA2 gene and the role of RAD26

RAD26; the yeast homologue of human CSB, has an essential role in transcrip tion-coupled repair (TCR), We have mapped the requisite of Rad26 for nucleo tide excision repair (NER) within the different regions of the yeast Saccha romyces cerevisiae MFAP gene at nucleotide resolution. Our results show tha t Rad26 is dispensable for enhanced NER in both the MFA2 upstream promoter, except in the TATA box region, and for enhanced NER in both strands of the active gene at a site close to the transcription termination region. As ex pected, it is not needed for repair of regions downstream of where transcri ption terminates. However, it is required for TCR in the transcription init iation and elongation regions. Our data support the hypothesis that Rad26 i s required for the interchange between holo-TFIIH and a putative repairosom e containing core TFIIH and other NER proteins. Close to the end of transcr iption, hotspots for the repair of CPDs in both the transcribed strand and the non-transcribed strand occur. This enhanced repair is independent of Ra d26. Hence, TFIIH may take a form favourable for forming a repairosome with out Rad26 assistance; here the organisation of the DNA during the terminati on of transcription may facilitate access of a repair complex to enable enh anced repair of both strands.