Coordinates the activities of more than 70 polypeptides required for initiation of transcription by RNA polymerase II
Binds to the core promoter to position the polymerase properly
Serves as the scaffold for assembly of the remainder of the transcription complex
Acts as a channel for regulatory signals
TFIID is itself composed of several subunits called TBP-associated factors (TAFs), In a test tube, only TBP is necessary for transcription at promoters that contain a TATA box.1 TAFs, however, add promoter selectivity, especially if there is no TATA box sequence for TBP to bind to. TAFs are included in two distinct complexes, TFIID2 and B-TFIID.3 The TFIID complex is composed of TBP and more than eight TAFs. But, the majority of TBP is present in the B-TFIID complex, which is composed of TBP and TAFII170 (BTAF1) in a 1:1 ratio.4 TFIID and B-TFIID are not equivalent, since transcription reactions utilizing TFIID are responsive to gene specific transcription factors such as SP1, while reactions reconstituted with B-TFIID are not.4
^Dynlacht, Brian David; Hoey, Timothy; Tjian, Robert (Aug 1991). "Isolation of co-activators associated with the TATA-binding protein that mediate transcriptional activation". Cell66 (3): 563–576. doi:10.1016/0092-8674(81)90019-2. PMID1907890.