PARP10 is critical for stress granule initiation.

Stress granules (SGs) are cytoplasmic biomolecular condensates enriched with RNA and translation factors. They form in response to stress, in part through phosphorylation of the translation initiation factor eIF2α, and are implicated in viral infection, tumorigenesis, and neurodegeneration. Although ADP-ribosylation plays a key role in SG assembly, the enzyme responsible for this ADP-ribosylation during SG assembly remains unidentified. Here, we systematically knock down the human ADP-ribosyltransferase family and identify PARP10 as pivotal for SG assembly. Live-cell imaging reveals PARP10's crucial role in regulating initial SG assembly kinetics. Further, we pinpoint the core SG component, G3BP1, as a PARP10 substrate and find that PARP10 regulates SG assembly via G3BP1 or a synthetic mimic that recapitulates its domain architecture. PARP10 knockdown reduces eIF2α phosphorylation and alters the SG core composition, notably decreasing translation factor presence. Based on our findings, we propose a model in which ADP-ribosylation acts as a rate-limiting step, initiating the formation of SGs.