Effects of Heat Stress on Yeast Heat Shock Factor-Promoter Binding In Vivo

Heat shock factor-DNA interaction is critical for understanding the regulatory mechanisms of stress-induced gene expression in eukaryotes. In this study, we analyzed the in vivo binding of yeast heat shock factor (H SF) to the promoters of target gene s ScSSA 1, ScSSA 4, HSP3 0 and HSP104, using chromatin immunoprecipitation. Previous work suggested that yeast HSF is constitutively bound to DNA at all temperatures. Expression of HSF target genes is regulated at the post-transcriptional level. However, our results indicated that HSF does not bind to the promoters of ScSSA4 and HSP30 at normal temperature (23 °C). Binding to these promoters is rapidly induced by heat stress at 39 °C. HSF binds to ScSSA1 and HSP104 promoters under non-stress conditions, but at a low level. Heat stress rapidly leads to a notable increase in the binding of HSF to these two genes. The kinetics of the level of HSF-promoter binding correlate well with the expression of target genes, suggesting that the expression of HSF target genes is at least partially the result of HSF-promoter binding stability and subsequent transcription stimulation.