HEAT-INDUCIBLE DNA FINDING OF PURIFIED HEAT-SHOCK TRANSCRIPTION FACTOR-1

The heat-induced expression of heat shock proteins, called the cellula r stress response, is mediated by heat shock transcription factor 1 (H SF1). HSF1 exists in unstressed cells in an inactive form, which is co nverted to the DNA binding form upon exposure of cells to elevated tem perature. We have developed a protocol for isolation of the non-DNA bi nding form of recombinant mouse HSF1, involving expression and affinit y purification of HSF1 as a fusion with the glutathione S-transferase protein in Escherichia coil, followed by specific protease cleavage to release pure HSF1 protein, We report here that the purified inactive HSF1 can be converted to the DNA binding form by heat treatment in vit ro, Chemical cross-linking analysis demonstrates that this conversion is accompanied by oligomerization of HSF1 from a monomeric to a trimer ic native structure, similar to that observed for HSF1 in heat-shocked cells, These results indicate that elements residing in the HSF1 poly peptide are sufficient both for maintenance of this factor in the non- DNA binding form and for its heat-induced conversion to the DNA bindin g form and support a role for HSF1 as the ''molecular thermostat'' in eukaryotic cells, which senses adverse environmental conditions and ac tivates the cellular stress response.