TFIIB is a single 33kDa polypeptide consisting of 316 amino acids. TFIIB is made up of four functional regions: the C-terminal core domain; the B linker; the B reader and the amino terminal zinc ribbon.
TFIIB makes protein-protein interactions with the TATA-binding protein (TBP) subunit of transcription factor IID, and the RPB1 subunit of RNA polymerase II.
TFIIB makes sequence-specific protein-DNA interactions with the B recognition element (BRE), a promoter element flanking the TATA element.