TATA binding protein

TBP (TATA Binding Protein) is a DNA binding protein that binds sequence specifically to the TATA box found in gene promoters.

TBP is vital for all eukaryote transcription, and will in some cases be forced to bind non sequence specifically. It is involved in DNA melting (double strand separation) and bends the DNA by 80° (the AT-rich sequence to which it binds facilitates easy melting). The TBP is an unusual protein in that it binds the minor groove using a β sheet.

Role as Transcription Factor Subunit
TBP is a subunit of the eukaryotic transcription factor TFIID. TFIID is the first protein to bind to DNA during the formation of the pre-initiation transcription complex of RNA polymerase II (RNA Pol II). Binding of TFIID to the TATA box in the promoter region of the gene initiates the recruitment of other factors required for RNA Pol II to begin transcription. Some of the other recruited transcription factors include TFIIA, TFIIB and TFIIF. Each of these transcription factors are formed from the interaction of many protein subunits, indicating that transcription is a heavily regulated process.

TBP is also a necessary component of RNA polymerase I and RNA polymerase III, and is perhaps the only common subunit required by all three of the RNA polymerases.

DNA-Protein Interactions
When TBP binds to a TATA box within the DNA, it distorts the DNA by inserting amino acid side chains between base pairs, partially unwinding the helix, and doubly kinking it. The distortion is accomplished through a great amount of surface contact between the protein and DNA. TBP binds with the negatively charged phosphates in the DNA backbone through positively charged lysine and arginine amino acid residues. The sharp bend in the DNA is produced through projection of four bulky phenylalanine residues into the minor groove. As the DNA bends, its contact with TBP increases, thus enhancing the DNA-protein interaction.

The strain imposed on the DNA through this interaction initiates melting, or separation, of the strands. Because this region of DNA is rich in adenine and thymine residues, which base pair through only two hydrogen bonds, the DNA strands are more easily separated. Separation of the two strands exposes the bases and allows RNA polymerase II to begin transcription of the gene.

For information on the use of TBP in cells see: RNA polymerase I, RNA polymerase II and RNA polymerase III.