Composition: TFIID is a multi-component (>5 subunits) transcription factor that recognizes and binds to the promoter DNA. TFIID consists of a DNA binding subunit that recognizes the TATA element and is therefore designated TATA-binding protein (or TBP), as well as several TBP-associated factors (or TAFs).
Interactions: TFIID acts to nucleate the transcription complex, recruiting the rest of the factors through a direct interaction with TFIIB. The TBP subunit of TFIID is sufficient for TATA element binding and TFIIB interaction, and can support basal transcription. However, this basal transcription reaction does not respond to upstream transcription activators. Many of these regulatory factors interact with TBP or TAFs in various in vitro assays. TBP also interacts directly with TFIIA.
Features: TBP consists of a 180 amino acid domain that is sufficient for activity. This domain is made up of an imperfectly repeated sequence, and the repeats are reflected in the symmetry of the molecule (see picture below). The protein resembles a saddle, with the inner surface contacting DNA and the outer surface presumable making protein-protein contacts.
Functions: TFIID binding is thought to be the first step in transcription initiation. Some of the TAFs also bind to initiator elements. TBP is also a component of the RNA polymerase I and RNA polymerase III transcription complexes.
This is picture of yeast TBP bound to DNA.
The coordinates for the yeast TBP cocrystal with DNA by Sigler group.
The coordinates for Arabidopsis thaliana TBP by Burley group.
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