TBP-associated factors

The general transcription factor TFllD is believed to be the key link between specific transcription factors and the general preinitiation complex. However, the purification and molecular characterization of TFllD from higher eucaryotes have been hampered by its instability and heterogeneity. All preparations of TFllD contain the TATA box-binding protein in combination with a variety of different proteins called TBP-associated factors, TAFs. When the preinitiation complex has been assembled, strand separation of the DNA duplex occurs at the transcription start site, and RNA polymerase II is released from the promoter to initiate transcription. However, TFIID can remain bound to the core promoter and support rapid reinitiation of transcription by recruiting another molecule of RNA polymerase. 

TBP binds to the TATA box in the minor groove of DNA (most transcription factors bind in the major groove) and causes an approximately 100-degree bend or kink of the DNA helix. This bending is thought to facilitate the interaction of TBP-associated factors with other components of the transcription initiation complex and possibly with factors bound to upstream elements. Although defined as a component of class II gene promoters, TBP, by virtue of its association with... 

TAF 250 TBP-Associated Factor II 250. Another direct connection between acetylation and transcriptional activation was demonstrated with the discovery that one of the TAFII (TATA-binding protein [TBP]-associated factor) subunits of the general transcription factor TFIID is itself a HAT. TFIID is one of the general factors required for the assembly of the RNA polymerase II transcription preinitiation... 

This consists of DNA-dependent RNA polymerase II and basal transcription factors (TFIIX, X = A - H). First, the basal factor TFIID binds to the promoter. TFIID, a large complex of numerous proteins, contains TATA boxbinding protein (TBP) and so-called TAFs (TBP-associated factors). The polymerase is attached to this core with the help of TFIIB. Before transcription starts, additional TFs have to bind, including TFIIH, which has heli-case activity and separates the two strands of DNA during elongation. In all, some 35 differ-... 

HRE - hormone response element TAFs - TBP-associated factors TBP - TATA box-binding protein A-H - basal transcription factors... 

The best-characterized coactivator is the transcription factor TFIID (Fig. 28-27). In eukaryotes, TFIID is a large complex that includes TBP and ten or more TBP-associated factors (TAFs). Some TAFs resemble histones and may play a role in displacing nucleosomes during the activation of transcription. Many DNA-binding transactivators aid in transcription initiation by interacting with one or more TAFs. The requirement for TAFs to initiate transcription can vary greatly from one gene to another. Some promoters require TFIID, some do not, and some require only subsets of the TFIID TAF subunits. 

Green, M.R. (2000) TBP-associated factors (TAFIIs) multiple, selective transcriptional mediators in common complexes. TrendsBiochem. Sci., 25, 59-63. 

Fig. 7. Model for activation by coactivators (A) and inhibition by corepressors (B) of transcription. Abbreviations CBP/p300, cAMP response element binding protein SRC-1, steroid receptor coactivator 1 TBP, TATA-binding protein TAF, TBP-associated factor pol II, RNA polymerase II N-CoR, nuclear receptor corepressor SMRT, silencing mediator of retinoic and thyroid hormone receptors.

Pol II is not the only target of Cdks. Cell-cycle kinases also control transcription by phosphorylation of TBPs and TBP-associated factors, TAFs although, at least in yeast, TAFs seem not to be obligatory for transcription. Tumour suppressors, such as p53, which are controlled by phosphorylation by Cdks, link transcription and the cell cyde. i Breakdown of transcriptional control by tumour suppressors is related to cancer. This is discussed in Part 4. 

Transversely alternating-field electrophoresis TBP-associated factors Triacyl glycerol Tosyl-arginine methyl ester... 

The TATA binding protein (TBP) is a universal eukaryotic transcriptional initiation protein that is required for the transcription of RNA pol I-dependent (rRNA), RNA pol II-dependent (mRNA and snRNA), and RNA pol Ill-dependent (tRNA and 55 rRNA) genes. Auxiliary proteins called TBP-associated factors (TAFs) provide promoter-selective properties to TBP and facilitate transcriptional regulation. 

Rudloff U., Eberhard D., Tora L., Stunnenberg H., Grummt I. (1994) TBP-associated factors interact with DNA and govern species specificity of RNA polymerase I transcription. EMBO J 13 2611. 

TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH are the general transcription factors. TFIID is also the TATA-box binding protein and is associated with TAFs (TBP associated factors). 

TFIID is one of the general transcription factors for RNA polymerase II. Part of it is a protein that binds to the TATA box in eukaryotic promoters. Associated in complex with the TATA box and the TBP are many proteins called TAFs, for TBP associated factors. 

Basal factors TFIID TAF1 Yeast-human H3 and H4 TBP-associated factor... 

---