Abstract
Transcriptional activation of heat shock genes is mediated by a presynthesized nuclear protein, the heat shock factor (HSF), which transiently converts from an inactive to an active form in response to hyperthermia. It has been suggested that hyperphosphorylation of HSF upon heat shock triggers activation through the induction of a conformational change unmasking transcriptional activator domains. Here we report that a short conserved element is involved in returning yeast HSF to the inactive state after heat shock and show that deactivation can be enhanced by phosphorylation of adjacent serine residues. These results suggest that phosphorylation of HSF in yeast serves as a regulatory mechanism to deactivate HSF, rather than being involved in its activation.