Initiation of transcription by RNA polymerase II requires the activities of more than 70 polypeptides. The protein complex that coordinates these activities is transcription factor IID (TFIID), which binds to the core promoter to position the polymerase properly, serves as the scaffold for assembly of the remainder of the transcription complex, and acts as a channel for regulatory signals. TFIID is composed of the TATA-binding protein (TBP) and a group of evolutionarily conserved proteins known as TBP-associated factors or TAFs. TAFs may participate in basal transcription, serve as coactivators, function in promoter recognition or modify general transcription factors (GTFs) to facilitate complex assembly and transcription initiation. This gene encodes one of the smaller subunits of TFIID that binds to the basal transcription factor GTF2B as well as to several transcriptional activators such as p53 and VP16. A similar but distinct gene (TAF9B) has been found on the X chromosome and a pseudogene has been identified on chromosome 19. Alternative splicing results in multiple transcript variants encoding different isoforms.
The 17-amino-acid-long trans-activating domains (TAD) of several transcription factors were reported to bind directly to TAF9: p53, VP16, HSF1, NF-IL6, NFAT1, NF-κB, and ALL1/MLL1. Inside of these 17 amino acids, a unique Nine-amino-acid transactivation domain (9aaTAD) was identified for each reported transcription factor. 9aaTAD is a novel domain common to a large superfamily of eukaryotic transcription factors represented by Gal4, Oaf1, Leu3, Rtg3, Pho4, Gln4, Gcn4 in yeast and by p53, NFAT, NF-κB and VP16 in mammals. TAF9 is supposed to be a universal transactivation cofactor for 9aaTAD transcription factors.
^Evans SC, Foster CJ, El-Naggar AK, Lozano G (April 1999). "Mapping and mutational analysis of the human TAF2G gene encoding a p53 cofactor". Genomics. 57 (1): 182–3. doi:10.1006/geno.1999.5745. PMID10191103.
^ abPiskacek S, Gregor M, Nemethova M, Grabner M, Kovarik P, Piskacek M (June 2007). "Nine-amino-acid transactivation domain: establishment and prediction utilities". Genomics. 89 (6): 756–68. doi:10.1016/j.ygeno.2007.02.003. PMID17467953.
^The prediction for 9aa TADs (for both acidic and hydrophilic transactivation domains) is available online from National EMBnet-Node Austria ("9aaTAD Prediction Webtool". EMBnet AUSTRIA. Retrieved 2009-01-10.)
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