Heat shock induces assembly of a protein complex that activates yeast SAPKs Mpk1 and Hog1.

Heat shock activates the yeast SAPK Mpk1 in Saccharomyces cerevisiae via additive top-down MEK-dependent and lateral Hog1-dependent pathways that converge on a CWI HS complex.

• Why it matters: Stress-activated protein kinases integrate many stress signals, but how heat shock engages the cell wall integrity pathway and coordinates Mpk1 with Hog1 was unclear.
• What they did: The study shows heat shock triggers Mpk1 activation through a top-down route requiring MEK activation and a lateral route that does not depend on MEKK regulation, both contributing additively. It also identifies a CWI HS complex where Hog1 is transiently recruited and activated.
• The result: Hog1 activation occurs within the complex, and Hog1 release requires its catalytic activity, implying Hog1 phosphorylates targets while bound to activate Mpk1 and then disengage.

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