The general transcription factor, TFIID, consists of the TATA-binding protein (TBP) associated with a series of TBP-associated factors (TAFs) that together participate in the assembly of the transcription preinitiation complex. This entry represents a conserved domain found at the C terminus of Transcription initiation factor TFIID subunit 11 from humans (also known as Transcription initiation factor TFIID 28 kDa subunit, TAFII28 []). TAF11 interacts with the ligand binding domains of the nuclear receptors for vitamin D3 and thyroid hormone []. It also interacts directly with TFIIA, acting as a bridging factor that stabilises the TFIIA-TBP-DNA complex []. The crystal structure of hTAFII28 with hTAFII18 shows that this region is involved in the binding of these two subunits. The conserved region contains four α-helices and three loops arranged as in histone H3 [, ].
This family includes the Spt3 yeast transcription factors and the 18kDa subunit from human transcription initiation factor IID, known as TAF13 or TAFII18. Determination of the crystal structure reveals an atypical histone fold [].TBP-associated factor 13 (TAF13) is one of several TAFs that bind TBP and is involved in forming the transcription factor IID (TFIID) complex. TAF13 interacts with TAF11 and makes a histone-like heterodimer similar to H3/H4-like proteins. The dimer may be structurally and functionally similar to the spt3 protein within the SAGA histone acetyltransferase complex [].TFIID is one of seven General Transcription Factors (GTF) (TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIID) that are involved in accurate initiation of transcription by RNA polymerase II in eukaryotes. TFIID plays an important role in the recognition of promoter DNA and assembly of the pre-initiation complex. TFIID complex is composed of the TBP and at least 13 TAFs. Each TAF, with the help of a specific activator, is required only for expression of subset of genes and is not universally involved for transcription as are GTFs. In yeast and human cells, TAFs have been found as components of other complexes besides TFIID. Several TAFs interact via histone-fold (HFD) motifs; the HFD is the interaction motif involved in heterodimerization of the core histones and their assembly into nucleosome octamers. The minimal HFD contains three α-helices linked by two loops and are found in core histones, TAFs and many other transcription factors. TFIID has a histone octamer-like substructure.
