Transcription factor II H (TFIIH) is one of several general transcription factor

General transcription factor

General transcription factors or basal transcription factors are protein transcription factors that have been shown to be important in the transcription of class II genes to mRNA templates...

s that make up the RNA polymerase II

RNA polymerase II

RNA polymerase II is an enzyme found in eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase...

 preinitiation complex

Preinitiation complex

The preinitiation complex is a large complex of proteins that is necessary for the transcription of protein-coding genes in eukaryotes...

. TFIIH consists of ten subunits, 7 of which (XPD, XPB, p62, p52, p44, p34 and TTDA) form the core complex. The cyclin activating kinase-subcomplex (CDK7, MAT1, and cyclin H) is linked to the core via the XPD protein Two of the subunits, ERCC2

ERCC2

ERCC2, or XPD is a protein involved in transcription-coupled nucleotide excision repair.The XPD gene encodes for a 2.3-kb mRNA containing 22 exons and 21 introns. The XPD protein is a 760 amino acids polypeptide with a size of 87kDa...

/XPD and ERCC3/XPB

XPB

XPB is an ATP dependent human DNA helicase that is a part of the TFIIH transcription factor complex.-Structure:The 3D structure of the archeael homologue of XPB has been solved by X-ray crystallography by Dr...

, have helicase

Helicase

Helicases are a class of enzymes vital to all living organisms. They are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands using energy derived from ATP hydrolysis.-Function:Many cellular processes Helicases are a...

 and ATPase

ATPase

ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate into adenosine diphosphate and a free phosphate ion. This dephosphorylation reaction releases energy, which the enzyme harnesses to drive other chemical reactions that would not otherwise occur...

 activities and help create the transcription bubble

Transcription bubble

A transcription bubble is a molecular structure that occurs during the transcription or replication of DNA when DNA helicase and DNA topoisomerase "unzip" the DNA double strand. DNA polymerase or RNA polymerase may then bind to the exposed DNA and begin synthesizing a new strand of DNA or RNA...

. In a test tube these subunits are only required for transcription if the DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 template is not already denatured or if it is supercoiled

DNA supercoil

DNA supercoiling refers to the over- or under-winding of a DNA strand, and is an expression of the strain on the polymer. Supercoiling is important in a number of biological processes, such as compacting DNA. Additionally, certain enzymes such as topoisomerases are able to change DNA topology to...

. Two other TFIIH subunits, CDK7 and cyclin H

Cyclin H

Cyclin-H is a protein that in humans is encoded by the CCNH gene.-Interactions:Cyclin H has been shown to interact with P53, Cyclin-dependent kinase 7 and MNAT1.-Further reading:...

, phosphorylate

Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

 serine

Serine

Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...

 amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s on the RNA polymerase II C-terminal domain and possibly other proteins involved in the cell cycle

Cell cycle

The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

. Next to a vital function in transcription initiation, TFIIH is also involved in nucleotide excision repair

Nucleotide excision repair

Nucleotide excision repair is a DNA repair mechanism. DNA constantly requires repair due to damage that can occur to bases from a vast variety of sources including chemicals, radiation and other mutagens...

.