TFIID
TFIID, the largest of the GTF’s,
is believed to be the first to bind to the promoter region of DNA (Buratowski,
1999). It comprises the large TATA box binding protein (TBP) along
with up to 7 other polypeptide sub-units, containing “an HMG box, bromodomains,
and a serine kinase” (Brody, 2001). It also appears to have histone
acetyltransferase (HAC) activity. It has been found to exist, like
a nucleosome, as a heteotetramer in solution, leading many to believe it
has a histone-octamer structure (Brody, 2001).
Using DNA footprinting experiments,
it was observed that TFIID bound and “protected” DNA from shearing at base
pairs –42 to –17, binding the TATA box at the promoter region at –25 (McClean,
1997).
Electron microscopy studies performed
in 1999 in the Lawrence Berkeley National Laboratory revealed the 3-D structure
of TFIID, including the TBP position and the position and structure of both
TFIIA and TFIIB within the complex. The 3-D model was created by first
recording the shape of thousands of randomly oriented protein complexes,
then aligning and merging those images with a computer. It yielded
a detailed picture with a resolution of 35 Angstroms, shown below (Yarris,
1999).
This picture reveals that TFIID is
a horseshoe-like structure and appears to bind DNA at the top of the shoe,
where antibodies indicate the TBP is located. It also indicates where
TFIIA and TFIIB interact with the complex.
Click on the following links to view a specific transcription factor.
TFIIA
, TFIIB
, TFIID
, TFIIE
, TFIIF
, TFIIH
, TFII I
, TFIIS
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