TFIID recruitment

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. 

Figure 37-10. Two models for assembly of the active transcription complex and for how activators and coactivators might enhance transcription. Shown here as a small oval is TBP, which contains TFIID, a large oval that contains all the components of the basal transcription complex illustrated in Figure 37-9 (ie, RNAPII andTFIIA,TFIIB, TFIIE,TFIIF, and TFIIFI). Panel A The basal transcription complex is assembled on the promoter after the TBP subunit of TFIID is bound to the TATA box. Several TAFs (coactivators) are associated with TBP. In this example, a transcription activator, CTF, is shown bound to the CAAT box, forming a loop complex by interacting with a TAF bound to TBP. Panel B The recruitment model. The transcription activator CTF binds to the CAAT box and interacts with a coactivator (TAF in this case). This allows for an interaction with the preformed TBP-basal transcription complex. TBP can now bind to the TATA box, and the assembled complex is fully active.

TFIID 13 Recognizes TATAbox recruits TFIIB (composed of factors TB P and TAFs)... 

TFIID (which contains the TATA-box binding protein, TBP) binds to the TATA box. TFIIA and TFIIB then bind, followed by recruitment of RNA polymerase II and TFIIF. TFIIH and TFIIE then bind to form the preinitiation complex (PIC). Kinases phosphorylate the C-terminal domain of Pol II, leading to the open complex in which the DNA strands are separated. RNA is produced during elongation as Pol II and TFIIF leave the promoter and the other general transcription factors behind. Pol II dissociates during the termination phase, and the CTD is dephosphorylated. Pol II/TFIIF is then recycled to bind to another promoter. 

New evidence indicates that the major mediators in remodeler recruitment may be bromo and chromo domain-containing proteins. Bromo domains mediate protein binding to acetyl-lysines in histones and other proteins (Jacobson et al., 2000), and chromo domains have been shown to bind methyl-lysines (Jacobs et al., 2002). For instance, TAF1, a component of TFIID, contains two tandem bromo domains that bind selectively to multiply acetylated H4 peptides (Jacobson et al., 2000). Furthermore, the Gcn5 bromo domain preferentially binds acetylated H4 K16 (Owen et al., 2000). 

TFIIB TFIID 35 1 RNAPII-TFIIF recruitment, start-site selection by RNAPII... 

HSE is needed for recruitment of the RNA polymerase to the heat-shock promoter. The binding of TFIID to the uninduced promoter may help heat-shock genes respond more rapidly to an increase in temperature. 

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