TATA Binding Protein (TBP) Associated Factor 9 (TAF9) is one of several TAFs that bind TBP and is involved in forming Transcription Factor IID (TFIID) complex
The TATA Binding Protein (TBP) Associated Factor 9 (TAF9) is one of several TAFs that bind TBP and are involved in forming the TFIID 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. The TFIID complex is composed of the TBP and at least 13 TAFs. TAFs from various species were originally named by their predicted molecular weight or their electrophoretic mobility in polyacrylamide gels. A new, unified nomenclature for the pol II TAFs has been suggested to show the relationship between TAFs orthologs and paralogs. Human TAF9 has a paralogue gene (TAF9L) which has a redundant function. Several hypotheses are proposed for TAF function such as serving as activator-binding sites, in core-promoter recognition or a role in essential catalytic activity. It has been shown that TAF9 interacts directly with different transcription factors such as p53, herpes simplex virus activator vp16 and the basal transcription factor TFIIB. Each TAF, with the help of a specific activator, is required only for expression of subset of genes and are not universally involved for transcription as are GTFs. In yeast and human cells, TAFs have been found as components of other complexes besides TFIID. TAF9 is a component of TFIID in multiple organisms as well as different TBP-free TAF complexes containing the GCN5-type histone acetyltransferase. Several TAFs interact via histone-fold (HFD) motifs; HFD is the interaction motif involved in heterodimerization of the core histones and their assembly into nucleosome octamers. The minimal HFD contains three alpha-helices linked by two loops and is found in core histones, TAFS and many other transcription factors. TFIID has a histone octamer-like substructure. TFIID has a histone octamer-like substructure. TAF9 is a shared subunit of both, histone acetyltransferase complex (SAGA) and TFIID complexes. TAF9 domain interacts with TAF6 to form a novel histone-like heterodimer that is structurally related to the histone H3 and H4 oligomer.