text: TFB is a single polypeptide, around 280 to 300 amino acids in length and 34 kDa in mass, that is required for the recruitment of RNA polymerase (RNAP) to begin transcription, and it may also affect the transcription complexs structure during changes that occur before transcription, though specific mechanisms are unknown. TFBs structure consists of an amino-terminal region (TFB) with conserved sequences and complex structures, linked to a larger, globular carboxyl-terminal region (TFB). While the N-terminal domain mediates the RNAP interactions, the C-terminal domain mediates interactions with complex formed of the TATA box and TBP, a DNA sequence and polypeptide involved with translation initiation. The degree of conservation of TFB's sequence throughout Archaea ranges from 50% to 60%. In respect to its eukaryotic equivalent, TFB shows "high levels of structural and functional conservation." The interactions between TBP and a sequence upstream of the TATA box governs transcription polarity, "yields an archaeal preinitiation complex," and orients the complex in the direction in which the target gene should be transcribed. The TBP shows an inverted orientation compared to the eukaryotic TFIIB.
  TFB makes up approximately one third of the protein and contains both a B-finger motif (homologous to the TFIIB B-finger) and a zinc-finger motif, the latter of which is located at amino acids 2-34. The N-terminal domain size varies from 100 to 120 amino acids in length. Crosslinking experiments have shown this domain is located close to the transcription start site. The zinc-finger interacts with the RNAP dock domain, and the B-finger may affect RNAP-promoter interactions. TFB contains motifs which interact with the TATA binding protein (TBP), the TFB-recognition elements (BRE) upstream of the TATA box, and sequences of DNA downstream of the TATA. Its size is approximately 180 amino acids, which is made up of two repeats of a 90-amino acid sequence. The C-terminal domain specifically may be what influences the direction of the preinitiation complex. Since TFB binds the RNAP and TFB binds the TBP-TATA complex, TBP connects the two.