Transcription factor II D

Transcription factor II D (TF_IID) is one of several general transcription factors that make up the RNA polymerase II preinitiation complex. 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. Before the start of transcription, the transcription Factor II D (TF_IID) complex binds to the core promoter DNA of the gene through specific recognition of promoter sequence motifs, including the TATA box, Initiator, Downstream Promoter, Motif Ten, or Downstream Regulatory elements.

Functions

• Coordinates the activities of more than 70 polypeptides required for initiation of transcription by RNA polymerase II
• Binds to the core promoter to position the polymerase properly
• Serves as the scaffold for assembly of the remainder of the transcription complex
• Acts as a channel for regulatory signals

Structure

TF_IID is itself composed of TBP and several subunits called TATA-binding protein Associated Factors (TBP-associated factors, or TAFs). 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, TF_IID and B-TF_IID. The TF_IID complex is composed of TBP and more than eight TAFs. But, the majority of TBP is present in the B-TF_IID complex, which is composed of TBP and TAFII170 (BTAF1) in a 1:1 ratio. TF_IID and B-TF_IID are not equivalent, since transcription reactions utilizing TF_IID are responsive to gene specific transcription factors such as SP1, while reactions reconstituted with B-TF_IID are not.

Subunits in the TF_IID complex include:

• TBP (TATA binding protein), or:
  • TBP-related factors in animals (TBPL1; TBPL2)
• 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)

See also

• Eukaryotic transcription
• General transcription factor
• Preinitiation complex
• Regulation of gene expression
• RNA polymerase II holoenzyme
• TATA binding protein
• Transcription (genetics)

External links

• Transcription+Factor+TFIID at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• 3D electron microscopy structures of TFIID from the EM Data Bank(EMDB)