Trimerization of a yeast transcriptional activator via a coiled-coil motif.

The transcriptional induction of heat shock genes is mediated by the heat shock transcription factor (HSF). We have investigated the oligomerization state of HSF from S. cerevisiae and find that it forms a trimer in solution and when bound to DNA. Trimerization is mediated by a region of HSF that, like the leucine zipper, is characterized by the occurrence of hydrophobic amino acids every 7 residues. We propose that it forms a three-stranded coiled coil.