The yeast heat shock transcription factor changes conformation in responseto superoxide and temperature

In vitro DNA-binding assays demonstrate that the heat shock transcription f actor (HSF) from the yeast Saccharomyces cerevisiae can adopt an altered co nformation when stressed. This conformation, reflected in a change in elect rophoretic mobility, requires that two HSF trimers be bound to DNA. Single trimers do not show this change, which appears to represent an alteration i n the cooperative interactions between trimers. HSF isolated from stressed. cells displays a higher propensity to adopt this altered conformation. Pur ified HSF can be stimulated in vitro to undergo the conformational change b y elevating the temperature or by exposing HSF to superoxide anion. Mutatio nal analysis maps a region critical for this conformational change to the f lexible loop between the minimal DNA-binding domain and the flexible linker that joins the DNA-binding domain to the trimerization domain. The signifi cance of these findings is discussed in the context of the induction of the heat shock response by ischemic stroke, hypoxia, and recovery from anoxia, all known to stimulate the production of superoxide.