TFIIH is a 10-protein complex that is conserved throughout eukaryotes. TFIIH has two primary cellular functions: transcription initiation and nucleotide excision repair (NER). NER in eukaryotes begins by recognition of a bulky lesion by the obligate dimer Rad4-Rad23. This is followed closely by the recruitment of TFIIH which is a structural scaffold, opens a bubble around damaged DNA and scans the damaged strand for bulky lesions. This facilitates the recruitment of two exonucleases which excise the damages strand before an undamaged complement is synthesize. In yeast (Saccharomyces cerevisiae), TFIIH is composed of the two helicases Ssl2 and Rad3, the scaffolding subunits Tfb1, Tfb2, Tfb4 and Ssl1 and the kinase subunits Kin28, Ccl1 and Tfb3, though these later 3 are dispensable for NER.