Transcription factor II D

RNA polymerase II holoenzyme is a form of eukaryotic RNA polymerase II that is recruited to the promoters of protein-coding genes in living cells. It consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as SRB proteins. Transcription factor II D (TFIID) is one of several general transcription factors that make up the RNA polymerase II preinitiation complex. Before the start of transcription, the transcription Factor II D (TFIID) complex, binds to the TATA box in the core promoter of the gene.

TFIID is itself composed of several subunits called TBP-associated factors (TAFs, of which there are 16) and the TATA Binding Protein (TBP). In a test tube, only TBP is necessary for transcription at promoters that contain a TATA box. TAFs, however, add promoter selectivity, especially if there is no TATA box sequence for TBP to bind to. TAFs are included in two distinct complexes, TFIID and B-TFIID. The TFIID complex is composed of TBP and more than eight TAFs. But, the majority of TBP is present in the B-TFIID complex, which is composed of TBP and TAFII170 (BTAF1) in a 1:1 ratio.

TFIID (GTF2D)
 * 1) coordinates the activities of more than 70 polypeptides required for iniation of transcription by RNA polymerase II,
 * 2) binds to the core promoter to position the polymerase properly,
 * 3) serves as the scaffold for assembly of the remainder of the transcription complex, and
 * 4) acts as a channel for regulatory signals.

Subunits in the TFIID complex include:
 * TBP (TATA binding protein)
 * TAF1 (TAFII250)
 * TAF2 (CIF150)
 * TAF3 (TAFII140)
 * TAF4 (TAFII130/135)
 * TAF4B (TAFII105)
 * TAF5 (TAFII100)
 * TAF6 (TAFII70/80)
 * TAF7 (TAFII55)
 * TAF8 (TAFII43)
 * TAF9 (TAFII31/32)
 * TAF9B (TAFII31L)
 * TAF10 (TAFII30)
 * TAF11 (TAFII28)
 * TAF12 (TAFII20/15)
 * TAF13 (TAFII18)
 * TAF15 (TAFII68)