GTF2B
Description
The GTF2B (general transcription factor IIB) is a protein-coding gene located on chromosome 1.
Transcription factor II B (TFIIB) is a general transcription factor that is involved in the formation of the RNA polymerase II preinitiation complex (PIC) and aids in stimulating transcription initiation. TFIIB is localised to the nucleus and provides a platform for PIC formation by binding and stabilising the DNA-TBP (TATA-binding protein) complex and by recruiting RNA polymerase II and other transcription factors. It is encoded by the TFIIB gene, and is homologous to archaeal transcription factor B and analogous to bacterial sigma factors.
== Structure == 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.
== Mechanism of action == There are six steps in the mechanism of TFIIB action in the formation of the PIC and transcription initiation:
RNA polymerase II is recruited to DNA through the TFIIB B core and B ribbon. RNA polymerase II unwinds DNA, aided by the TFIIB B linker and B reader (open complex formation). RNA polymerase II selects a transcription start site, aided by the TFIIB B reader. RNA polymerase II forms the first phosphodiester bond.
GTF2B is a general transcription factor that plays a key role in initiating transcription by RNA polymerase II (Pol II). It participates in the formation of the pre-initiation complex (PIC) and recruits Pol II to the promoter DNA. GTF2B, in conjunction with the TATA box-bound TBP, forms the core initiation complex, acting as a bridge between TBP and the Pol II-TFIIF complex. Following the start of transcription, during the transition from initiation to elongation, GTF2B is released from the PIC and re-associates with TBP during the next round of transcription. GTF2B binds to chromatin at specific core promoter regions. It binds to two distinct DNA core promoter consensus sequence elements, independent of TBP. These elements, called IIB-recognition elements (BREs), are located immediately upstream (BREu) and downstream (BREd) of the TATA box element. GTF2B influences the selection of the transcription start site and exhibits autoacetyltransferase activity, contributing to activated transcription.
GTF2B is also known as TF2B, TFIIB.
