DNA RECOGNITION BY PROTEIN COMPLEXES DURING EUKARYOTIC TRANSCRIPTION INITIATION. Stephen K. Burley, The Rockefeller University and Howard Hughes Medical Institute, New York, New York, USA

The TATA box-binding protein (TBP) is required by all three eukaryotic RNA polymerases for correct initiation of transcription of ribosomal, messenger, small nuclear and transfer RNAs. In the most general case, pol II transcription of mRNA begins with TBP-mediated recognition of a TATA box located immediately upstream of the transcription start site. The structure of a TBP from Arabidopsis thaliana complexed with a fourteen base pair oligonucleotide bearing the Adenovirus major late promoter (AdMLP) TATA element has been determined at 1.9Å resolution. Binding of the monomeric, saddle-shaped protein induces an unprecedented conformational change in the DNA. Insertion of two pairs of phenylalanine side chains into two base steps (TpA and ApG) produces two sharp kinks at either end of the sequence TATAAAAG. Between the kinks the double helix is partially unwound and smoothly bent, approximating the widened minor groove face of the TATA element to the concave surface of the molecular saddle. More recently, the structure of a ternary complex of transcription factor IIB (TFIIB), TBP, and the AdMLP TATA element has been determined at 2.7Å resolution. The C-terminal/core region of TFIIB consists of two quasi-identical helical domains, separated by a cleft that grasps TBP's acidic C-terminal stirrup. The structure of the TBP-DNA complex is essentially unaffected by contact with the basic surface of core TFIIB, which also interacts with the phospho-ribose backbone up- and downstream of the center of the TATA element. The N-terminal domain of core TFIIB is located on the downstream surface of the ternary complex, where it could interact with RNA polymerase II and help fix the transcription start site. The upper surface and N-terminal stirrup of TBP, and the remaining surfaces of core TFIIB are available for interactions with TBP-associated factors, other class II initiation factors, and transcriptional activators and coactivators.