A history of TFIIH: two decades of molecular biology on a pivotal transcription/repair factor.

The TFIIH multiprotein complex is organized into a 7-subunit core associated with a 3-subunit CDK-activating kinase module (CAK). Three enzymatic subunits are present in TFIIH, two ATP-dependent DNA helicases: XPB and XPD, and the kinase Cdk7. Mutations in three of the subunits, XPB, XPD and TTDA, lead to three distinct genetic disorders: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD) predisposing patients not only to cancer and ageing but also to developmental and neurological defects. These heterogeneous phenotypes originate from the dual role of TFIIH in transcription and DNA repair. For twenty years, many molecular studies have been conducted with the aim to unveil the role of TFIIH in DNA repair and transcription as well as the origin of the phenotypes of patients. This review intends to give a non-exhaustive survey of the most prominent discoveries on the molecular functioning of TFIIH.