MODEL OF THE COMPLEX FORMED BETWEEN THE H2 DOMAIN OF THE TATA BOX-BINDING PROTEIN AND THE L(281-301) FRAGMENT OF THE HUMAN TRANSCRIPTION FACTOR TFIIA

Additional interactions possibly involving the well-exposed H2 helical domain of hTBP and the acidic fragment L(281-301) of the non-conserve d domain of hTFIIA have been proposed to account for the apparent disc repancies between the results of mutagenesis experiments on human prot eins and the structure of the ternary complex TBP/ TATA box/TFIIA esta blished from yeast proteins by X-ray crystallography. To verify this h ypothesis both peptides were synthesized and their structures studied by circular dichroism (CD), NMR and molecular modelling. These peptide s exist preferentially under helical conformations in solution (30% TF E in H2O). An interaction between the two peptides was observed by flu orescence (K-app 170 mu M), CD and NMR techniques. Molecular modelling studies indicate that this complex could be stabilized by electrostat ic interactions involving the glutamate Glu287 and aspartates (Asp290, Asp294, Asp297 and Asp298) of L(281-301)TFIIA and lysine residues (Ly s133, Lys138 and Lys145) and arginine residues (Arg137, Arg140) of H2( TBP) in agreement with mutagenesis experiments. Similar studies could now be carried out with human proteins to demonstrate the biological r elevance of this interaction.