SOLUTION STRUCTURE OF THE DNA-BINDING DOMAIN OF THE TOMATO HEAT-STRESS TRANSCRIPTION FACTOR HSF24

Two-dimensional-NMR and three-dimensional-NMR experiments were perform ed to determine the solution structure of the DNA-binding domain of th e tomato heat-stress transcription factor HSF24. Samples of uniformly N-15-labeled and N-15,C-13-labeled recombinant proteins were used in t he investigation. A near-complete assignment of the backbone H-1, N-15 and C-13 resonances was obtained by three-dimensional triple-resonanc e experiments, whereas three-dimensional ronuclear-single-quantum-corr elation-spectroscopy, HCCH-COSY and HCCH-TOCSY spectra were recorded f or side-chain assignments. 885 non-redundant distance constraints from two-dimensional-homonuclear and three-dimensional-N-15-edited and C-1 3-edited NOESY spectra and 40 hydrogen-bond constraints from exchange experiments were used for structure calculations. The resulting three- dimensional structure contains a three-helix bundle and a small four-s tranded antiparallel beta-sheet that forms a hydrophobic core. The two C-terminal helices are parts of a highly conserved helix-turn-helix m otif that is probably involved in DNA recognition and binding. In cont rast to heat-stress factors from yeast and animals, the plant heat-str ess factors lack a loop of 11 amino acid residues inserted between bet a 3 and beta 4. This leads to a tight turn between these beta-strands.