TFIID

TFIID (also known as transcription factor II D) is a multi-subunit general transcription factor involved in the formation of the pre-initiation complex (Hartl, 2009, p.406) TFIID binding is involved in the first step of transcription in eukaryotes. It later goes on to associate with RNA polymerase II , which is used to transcribe mRNA.

Structure

TFIID is comprised of a TATA-binding protein (TBP) and a complex of 10 TBP-associated factors (TAFs). The TBP region is required by all three RNA polymerases, whereas the TAF regions differ by RNA polymerase . TBP is composed of 180 amino acid residues and is highly conserved throughout evolution .

Mechanism

TBP recognises and binds to the TATA box in eukaryotic genes as per it's main function . The TAF subunits are not required in genes with a TATA promoter, however they do have a role in reducing transcription levels by dissociating TBP from the TATA box .

Unlike other proteins with DNA binding domains, TBP notably alters the structure of DNA when bound via twisting and bending it . This creates a hydrophobic exposed region for TFIIB to join to in the next step of pre-initiation complex formation .

Function

While the main function of the TBP region of TFIID is to bind to the TATA box on DNA, the TAF proteins have a range of functions. Notably, TAFII250 acts as a scaffold protein and has kinase activity, and TAFII150 binds to DNA downstream of the TATA box . Furthermore, TAFII80, TAFII31 and TAFII20 have show similar features and structures to histones H4, H3 and H2b respectively .

 

Gupta, P.K., 2007. Genetics; Classical to Modern. 1st ed. Rastogi Publications.

Hartl, D.L., Jones, E.W., 2009. Genetics; Analysis of Genes and Genomes. 7th ed. Jones and Bartlett Publications.

White, R.J., 2001. Gene Transcription; Mechanisms and Control. 1st ed. Blackwell Science Ltd.