Purification and characterization of a heat‐shock element binding protein from yeast.

The promoters of heat shock genes are activated when cells are stressed. Activation is dependent on a specific DNA sequence, the heat‐shock element (HSE). We describe the purification to homogeneity of an HSE‐binding protein from yeast (Saccharomyces cerevisiae), using sequential chromatography of whole cell extracts on heparin‐agarose, calf thymus DNA‐Sepharose and an affinity column consisting of a repetitive synthetic HSE sequence coupled to Sepharose. The protein runs as a closely spaced doublet of approximately 150 kd on SDS‐polyacrylamide gels; mild proteolysis generates a stable 70‐kd fragment which retains DNA binding activity. The relative affinities of the protein for a range of variant HSE sequences correlates with the ability of these sequences to support heat‐inducible transcription in vivo, suggesting that this polypeptide is involved in the activation of heat‐shock promoters. However, the protein was purified from unshocked yeast, and may therefore represent an unactivated form of heat‐shock transcription factor. Study of the purified protein should help to define the mechanistic basis of the heat‐shock response.