TAF5_NTD2 is the second conserved N-terminal region of TATA Binding Protein (TBP) Associated Factor 5 (TAF5), involved in forming Transcription Factor IID (TFIID)
The TATA Binding Protein (TBP) Associated Factor 5 (TAF5) is one of several TAFs that bind TBP and are involved in forming Transcription Factor IID (TFIID) complex. TAF5 contains three domains, two conserved sequence motifs at the N-terminal and one at the C-terminal region. TFIID is one of seven General Transcription Factors (GTF) (TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIID) 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 preinitiation complex. TFIID complex is composed of the TBP and at least 13 TAFs. In yeast and human cells, TAFs have been found as components of other complexes besides TFIID. TAF5 may play a major role in forming TFIID and its related complexes. 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 TAF orthologs and paralogs. TAF5 has a paralog gene (TAF5L) which has a redundant function. Several hypotheses are proposed for TAFs functions such as serving as activator-binding sites, core-promoter recognition or a role in essential catalytic activity. C-terminus of TAF5 contains six WD40 repeats that likely form a closed beta propeller structure and may be involved in protein-protein interaction. The first part of the TAF5 N-terminal (TAF5_NTD1) homodimerizes in the absence of other TAFs. The second conserved N-terminal part of TAF5 (TAF5_NTD2) has an alpha-helical domain. One study has shown that TAF5_NTD2 homodimerizes only at high concentration of calcium but not any other metals. No dimerization was observed in other structural studies of TAF_NTD2. 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 octamer. However, TAF5 does not have a HFD motif.