Signaling by the integrated stress response kinase PKR is fine-tuned by dynamic clustering
The double-stranded RNA sensor kinase PKR is one of four integrated stress response (ISR) sensor kinases that phosphorylate the alpha subunit of the eukaryotic initiation factor 2 (eIF2) in response to stress. The current model of PKR activation considers the formation of back-to-back PKR dimers as a prerequisite for signal propagation. Here we show that PKR signaling involves the assembly of dynamic PKR clusters. PKR clustering is driven by ligand binding to PKRs sensor domain and by front-to-front interfaces between PKRs kinase domains. PKR clusters are discrete, heterogeneous, autonomous coalescences that share some protein components with processing bodies. Strikingly, eIF2 is not recruited to PKR clusters, and PKR cluster disruption enhances eIF2 phosphorylation. Together, these results support a model in which PKR clustering buffers downstream signaling, which may enable proofreading the ISR.