THE YEAST TFB1 AND SSL1 GENES, WHICH ENCODE SUBUNITS OF TRANSCRIPTIONFACTOR IIH, ARE REQUIRED FOR NUCLEOTIDE EXCISION-REPAIR AND RNA-POLYMERASE-II TRANSCRIPTION

The essential TFB1 and SSL1 genes of the yeast Saccharomyces cerevisia e encode two subunits of the RNA polymerase II transcription factor TF IIH (factor b). Here we show that extracts of temperature-sensitive mu tants carrying mutations in both genes (tfb1-101 and ssl1-1) are defec tive in nucleotide excision repair (NER) and RNA polymerase II transcr iption but are proficient for base excision repair. RNA polymerase II- dependent transcription at the CYC1 promoter was normal at permissive temperatures but defective in extracts preincubated at a restrictive t emperature. In contrast, defective NER was observed at temperatures th at are permissive for growth. Additionally, both mutants manifested in creased sensitivity to UV radiation at permissive temperatures. The ex tent of this sensitivity was not increased in a tfb1-101 strain and wa s only slightly increased in a ssl1-1 strain at temperatures that are semipermissive for growth. Purified factor TFIIH complemented defectiv e NER in both tfb1-101 and ssl1-1 mutant extracts. These results defin e TFB1 and SSL1 as bona fide NER genes and indicate that, as is the ca se with the yeast Rad3 and Ssl2 (Rad25) proteins, Tfb1 and Ssl1 are re quired for both RNA polymerase II basal transcription and NER. Our res ults also suggest that the repair and transcription functions of Tfb1 and Ssl1 are separable.