TFIIA interacts with theTBP subunit ofTFIID and aids in the binding of TBP toTATA-box containingpromoter DNA.[2][3] Interaction of TFIIA with TBP facilitates formation of and stabilizes thepreinitiation complex. Interaction of TFIIA with TBP also results in the exclusion of negative (repressive) factors that might otherwise bind to TBP and interfere with PIC formation. TFIIA also acts as acoactivator for some transcriptionalactivators, assisting with their ability to increase, or activate, transcription. The requirement for TFIIAin vitro transcription systems has been variable, and it can be considered either as a GTF and/or a loosely associated TAF-like coactivator. Genetic analysis inyeast has shown that TFIIA is essential for viability.
TFIIA is a heterodimer with twosubunits: one large unprocessed (subunit 1, or alpha/beta; gene nameGTF2A1) and one small (subunit 2, or gamma; gene nameGTF2A2).[4][5] It was originally believed to be a heterotrimer of an alpha (p35), a beta (p19) and a gamma subunit (p12). In humans, the sizes of the encoded proteins are approximately 55 kD and 12 kD. Both genes are present in species ranging from humans to yeast, and their protein products interact to form acomplex composed of abeta barreldomain and analpha helical bundle domain. It is theN-terminal andC-terminal regions of the large subunit that participate in interactions with the small subunit. These regions are separated by another domain whose sequence is always present in large subunits from various species but whose size varies and whose sequence is poorlyconserved. A second gene encoding a large TFIIA subunit has been found in some highereukaryotes. This gene, ALF/TFIIAtau (gene nameGTF2A1LF) is expressed only inoocytes andspermatocytes, suggesting it has a TFIIA-like regulatory role for gene expression only ingerm cells.
^Høiby T, Zhou H, Mitsiou DJ, Stunnenberg HG (2007). "A facelift for the general transcription factor TFIIA".Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression.1769 (7–8):429–36.doi:10.1016/j.bbaexp.2007.04.008.hdl:2066/34866.PMID17560669.
