TFIIA
TFIIA is thought to be the next protein
to bind to the transcription-initiation complex. It joins
TFIID
and TBP at the promoter, where footprinting indicates it covers base pairs
from –80 to –17 from the start site for transcription (McClean, 1997).
The structure of this protein varies
slightly from species to species; it has 2 very acidic sub-units in yeast,
and 3 in drosophila and humans (Buratowski, 2001). The Richmond lab,
using x-ray crystallography, has determined the structure of a complex involving
TFIIA at a resolution of 2.5 Angstroms. It appears to have a boot-shaped
core containing 2 separate parts: 1 contains a ß barrel, the other
is a bundle of 4 alpha-helices (Richmond, 1999).
This picture indicates that the top
of the “boot” (the β barrel) binds TBP through interaction between the β
sheets in the boot and the β sheets in the TBP. This stabilizes the
interaction between the TBP and DNA. The top corner of the β barrel
also binds to the severely kinked DNA bound to the TBP. The bundle
of alpha-helices stick out into solution, and are believed to interact with
other proteins (Richmond, 1999).
TFIIA has an anti-repressor effect – it stabilizes the TBP-TFIID-DNA complex
by blocking repressor binding (McClean, 1997).
There is also an image created by
electron microscopy in the Lawrence Berkeley National Laboratory that indicates
where TFIIA binds in relation to the TFIID complex (Yarris, 1999).
Click on the following links to view a specific transcription factor.
TFIIA
, TFIIB
, TFIID
, TFIIE
, TFIIF
, TFIIH
, TFII I
, TFIIS
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