TFII – H has nine subunits (Roeder, 1996).  Its primary function is to initiate transcription and repair DNA damage (Bradsher et al, 2000).  TFII-H can perform enzymatic activities, acting as a DNA helicase and an ATP kinase (Papavassiliou, 1997).  During transcription initiation, a stable preinitiation complex (PIC) is completed by the binding of TFII – H (Bradsher et al, 2000).  The two largest subunits of TFII-H, XPB and XPD, are responsible for performing enzymatic activities to initiate transcription by melting the promoter regions around the transcription origin (Winkler et al, 2000).  The melting of the promoter region is ATP-dependent; TFII-H is important since it is the only transcription factor that is capable of ATP kinase activity (Hampsey, 1998).  Moreover, TFII-H can phosphorylate the carboxyl terminal domain (CTD) of RNA pol II, facilitating transcription elongation (Winkler et al, 2000 and Weaver, 2002).

TFII –H can also repair damaged DNA by nucleotide excision repair (NER) (Hampsey, 1998 and Winkler et al, 2000).  The helicase activities of XPB and XPD allow recognition and removal of DNA damage (Winkler et al, 2000).  Any mutations or defects in XPB and XPD can cause diseases such as xeroderma pigmentosum, Cockayne’s syndrome and trichothiodystrophy (Bradsher et al, 2000 and Winkler et al, 2000).      
Structure of the the Human Tfiih Mat1 subunit, the N-terminal domain
Primary citation: Gervais, V., Wasielewski, E., Busso, D., Poterszman, A., Egly, J. M., Thierry, J. C., Kieffer, B.: Solution Structure of the N-Terminal Domain of the Human Tfiih MAT1 Subunit: New Insights Into the Ring Finger Family To be Published

Image on this page was obtained from the Structure database from the NCBI Website.
The image was  captured using Cn3D 3.0

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