TATA-binding protein is a ubiquitously expressed nuclear protein that functions at the core of the general transcription factor protein complex TFIID. TFIID, which contains TBP and 13 TBP-associated factors , contributes to the formation of the transcription pre-initiation complex, an assembly of multiple protein complexes that bind to a gene promoter during the initiation of transcription . Once the pre-initiation complex is formed, RNA polymerase II becomes competent for elongation and transcribes the body of a gene. TBP functions in the recruitment of TFIID by binding to the TATA-box sequence found approximately 25 base pairs upstream of the transcription start site of many protein-coding genes. In addition, many transcriptional activator proteins interact with TBP and various TAF proteins to facilitate recruitment of TFIID and formation of the pre-initiation complex.