Biochemistry/BIMS 503

Protein-DNA complexes: TFIIA and TFIIB binding to TBP-DNA

David Auble

The TBP-DNA complex provides a scaffold for assembly of other factors at the promoter. Here you can see how the general transcription factors TFIIA and TFIIB form ternary complexes with TBP and DNA. The images are derived from 1nh2 (yeast TFIIA-TBP-DNA) and 1c9b (human TFIIB-TBP-DNA). TFIIA is a complex of large (Toa1) and small (Toa2) subunits. The central portion of Toa1 is not required for formation of TFIIA, and in the TFIIA-TBP-DNA complex shown here, TFIIA is composed of N- and C-terminal fragments of Toa1 (both shown in cyan) and the small subunit, Toa2 (magenta). In contrast, TFIIB is a single subunit (green). If you hover the cursor over portions of TBP in proximity to TFIIA and TFIIB, you can see that TFIIA and TFIIB interact with roughly opposite sides of TBP. This is consistent with the biochemical detection of TFIIA-TFIIB-TBP-DNA complexes, although the structure of this quaternary complex has not been determined directly.

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