Yeast heat shock factor contains separable transient and sustained response transcriptional activators

The transcriptional induction of heat shock genes in eukaryotes is mediated by the heat shock transcription factor (HSF). In yeast, this induction appears to involve the phosphorylation of DNA-bound factor. I report here that HSF contains two distinct transcriptional activation regions. In response to a temperature upshift, an N-terminal region mediates transient increases in HSF activity and a C-terminal region is essential for sustained increases. These sustained and transient activities are regulated over different temperature ranges, and increases in both are associated with rises in the level of HSF phosphorylation. I propose that the two HSF activation regions are regulated independently in response to different stimuli.