The multiple roles of transcription/repair factor TFIIH.

TFIIH is by far the most complex of the basal RNA polymerase II transcription factors. It is a protein kinase, a bi-directional DNA helicase and is essential for both transcription and nucleotide excision repair (NER). Furthermore, the factor can activate cyclin-dependent kinases and so might play a role in cell-cycle regulation. The recent elucidation of the subunit composition of TFIIH has shown an extraordinary conservation of its structure from yeast to human.