Overview
The TATA box has the core DNA sequence 5'-TATAAA-3' or a variant, which is usually followed by three or more adenine bases. It is usually located 25 base pairs upstream of the transcription site. The sequence is believed to have remained consistent throughout much of the evolutionary process, possibly originating in an ancient eukaryotic organism.
It is normally bound by the TATA binding protein (TBP) in the process of transcription, which unwinds the DNA, and bends it through 80°. The AT-rich sequence facilitates easy unwinding (due to weaker base-stacking interactions among A and T than G and C). The TBP is an unusual protein in that it binds to the minor groove and binds with a β sheet.
The TATA box is usually found at the binding site of RNA polymerase II. TFIID, a transcription factor, binds to the TATA box, followed by TFIIA binding to the upstream part of TFIID. TFIIB can then bind to the downstream part of TFIID. The polymerase can then recognize this multi-protein complex and bind to it, along with various other transcription factors such as TFIIF, TFIIE and TFIIH. Transcription is then initiated, and the polymerase moves along the DNA strand, leaving TFIID and TFIIA bound to the TATA box. These can then facilitate the binding of additional RNA polymerase II molecules.
This cluster of RNA polymerase II and various transcription factors is known as a basal transcriptional complex (BTC). In this state, it only gives a low level of transcription. Other factors must stimulate the BTC to increase transcription levels. One such example of a BTC stimulating region of DNA is the CAAT box.
Most genes lack a TATA box and use an initiator element or downstream core promoter (DCE) instead. Nevertheless, TBP is always involved and is forced to bind without sequence specificity. A genome-wide study put the fraction of TATA-dependent human promoters at ~10%. An earlier study of ~1,000 genes found 32% of the promoters had a TATA box.
Read more about this topic: TATA Box