Stress granule (SG) assembly represents a conserved eukaryotic defense strategy 
against various insults. Although essential for the ability to cope with 
deleterious conditions, the signaling pathways controlling SG formation are not 
fully understood. The energy sensor AMP-activated protein kinase (AMPK) is 
critical for the cellular stress response. Human cells produce two AMPK 
catalytic α-subunits with not only partially overlapping, but also unique 
functions. Here, we provide direct support for structural and functional links 
between AMPK-α isoforms and SGs. As such, several stressors promote SG 
association of AMPK-α2, but not AMPK-α1. Multiple lines of evidence link AMPK 
activity to SG biogenesis. First, pharmacological kinase inhibition interfered 
with SG formation. Second, AMPK-α knockdown combined with in-depth quantitative 
SG analysis revealed isoform-specific changes of SG characteristics. Third, 
overexpression of mutant α-subunits further substantiated that AMPK regulates SG 
parameters. Finally, we identified the SG-nucleating protein G3BP1 as an AMPK-α2 
binding partner. This interaction is stimulated by stress and notably occurs in 
SGs. Collectively, our data define the master metabolic regulator AMPK as a 
novel SG constituent that also controls their biogenesis.