NMR EVIDENCE FOR SIMILARITIES BETWEEN THE DNA-BINDING REGIONS OF DROSOPHILA-MELANOGASTER HEAT-SHOCK FACTOR AND THE HELIX-TURN-HELIX AND HNF-3 FORKHEAD FAMILIES OF TRANSCRIPTION FACTORS/

Heteronuclear multidimensional NMR experiments of residues 33-163 of t he DNA-binding domain of Drosophila heat shock factor, dHSF(33-163), w ere recorded, using only 3 mg of uniformly N-15-labeled or 2 mg of uni formly N-15/C-13-labeled protein. The polypeptide consists of a struct ured part comprising three helices, a three-stranded antiparallel beta -sheet, with the first two strands connected by a four-residue type I tight turn. The second helix is disrupted at its C-terminal end by a p roline residue and is followed by an extended turn, leading to the thi rd helix. The dHSF(33-163) protein is unstructured at its N- and C-ter mini, and a third unstructured region is found from Thr113 to Arg124. Exchange broadening of the N-15-H-1 correlations upon titration of N-1 5 labeled HSF with a 13-base-pair DNA duplex suggests a DNA-binding mo tif in which the third helix acts as the recognition helix. Both the s econdary structure and DNA-binding pattern of dHSF(33-163) suggest tha t the overall topology resembles that the helix-turn-helix bacterial a ctivator CAP [Weber, 1. T., & Steitz, T. A. (1987) J. Mol. Biol. 198, 311-326] and the liver-specific transcription factor HNF-3gamma, the p rototype of the HNF-3/forkhead protein family [Clark, K. L., Halay, E. D., Lai, E., & Burley, S. K. (1993) Nature 364, 412-420].