TBP-associated factor
The TBP-associated factors are proteins that associate with the TATA-binding protein in transcription initiation. It is a part of the transcription initiation factor TFIID multimeric protein complex. It also makes up many other factors, including SL1. They mediate the formation of the transcription preinitiation complex, a step preceding transcription of DNA to RNA by RNA polymerase II.
TAFs have a signature N-terminal histone-like fold domain. This domain is implicated in the pairwise interaction among specific TAFs.
Function
TFIID
TFIID plays a central role in mediating promoter responses to various activators and repressors. It binds tightly to TAFII-250 and directly interacts with TAFII-40. TFIID is composed of TATA binding protein and a number of TBP-associated factors.TAF is part of the TFIID complex, and interacts with the following:
- Specific transcriptional activators
- Basal transcription factors
- Other TAFIIs
- Specific DNA sequences, for example the promoter element">promotor (biology)">promoter element or gene-specific core promoter sequence
Some pairs of TAF interact with each other to form "lobes" in TFIID. Pairs known or suggested to exist in TFIID include TAF6-TAF9, TAF4-TAF12, TAF11-13, TAF8-TAF10 and TAF3-TAF10.
SL1
Selective factor 1 is composed of the TATA-binding protein and three TAF subunits. These TAFs do not have a histone-like fold domain.Other complexes
TAF is a part of SAGA and related coactivation complexes. Such complexes acetylate histone tails to activate genes. Human has three SAGA-like complexes: PCAF, TFTC, and STAGA. PCAF and KAT2A are two human homologs of the yeast Gcn5.TAF8, TAF10, and SPT7L forms a small TAF complex called SMAT.