InterPro domain: IPR035935

This entry represents TTDA/Tfb5 subunit of TFIIH basal transcription factor complex. These proteins have a structural motif consisting of a 2-layer sandwich structure with an alpha/beta plait topology. Nucleotide excision repair is a major pathway for repairing UV light-induced DNA damage in most organisms.

Transcription/repair factor IIH (TFIIH) is essential for RNA polymerase II transcription and nucleotide excision repair. The TFIIH multiprotein complex consists of a 7-subunit core (XPB, p62, p52, p44, p34, and TTDA) that is associated with a 3-subunit CDK-activating kinase module (MAT1, cyclin H and Cdk7) [ 1 ].

In humans, defects in TTDA cause the trichothiodystrophy photosensitive (TTDP), an autosomal recessive disease characterised by sulfur-deficient brittle hair and nails, ichthyosis, mental retardation, impaired sexual development, abnormal facies and cutaneous photosensitivity correlated with a nucleotide excision repair (NER) defect [ 2 ].

1. A history of TFIIH: two decades of molecular biology on a pivotal transcription/repair factor. DNA Repair (Amst.) 10, 714-21
2. A new, tenth subunit of TFIIH is responsible for the DNA repair syndrome trichothiodystrophy group A. Nat. Genet. 36, 714-9