DIFFERENT FORMS OF TFIIH FOR TRANSCRIPTION AND DNA-REPAIR - HOLO-TFIIH AND A NUCLEOTIDE EXCISION REPAIROSOME

Yeast TFIIH that is active in transcription can be dissociated into th ree components: a 5-subunit core, the SSL2 gene product, and a complex of 47 kDa, 45 kDa, and 33 kDa polypeptides that possesses protein kin ase activity directed towards the C-terminal repeat domain of RNA poly merase II. These three components can reconstitute fully functional TF IIH, and all three are required for transcription in vitro. By contras t, TFIIH that is highly active in nucleotide excision repair (NER) lac ks the kinase complex and instead contains the products of all other g enes known to be required for NER in yeast: RAD1, RAD2, RAD4, RAD10, a nd RAD14. This repairosome is not active in reconstituted transcriptio n in vitro and is significantly more active than any of the constituen t polypeptides in correcting defective repair in extracts from strains mutated in NER genes.