Abstract

Cells must respond rapidly to heat stress by activating multiple signaling pathways that preserve proteostasis. In budding yeast, this includes induction of Hsf1 and Msn2/4-mediated transcription, cell integrity signaling, stress-triggered phase separation of proteins, and inhibition of translation. How these pathways are so rapidly activated and coordinated remains unclear. We show that the mechanosensor Mid2 senses heat-induced membrane stretch and leads to rapid phosphorylation of the cytosolic Hsp70 Ssa1 at a well-conserved threonine (T492). Phosphorylation of T492 leads to epichaperome rearrangement promoting fine-tuning of multiple cellular processes including translational pausing, HSF activity, MAPK signaling and stress granule resolution. Taken together, these results provide a comprehensive, unified theory of the global yeast heat shock response mediated by the Hsp70 chaperone code.