The stress granule protein G3BP1 promotes pre‐condensation of cGAS to allow rapid responses to DNA

Cyclic GMP‐AMP synthase (cGAS) functions as a key sensor for microbial invasion and cellular damage by detecting emerging cytosolic DNA. Here, we report that GTPase‐activating protein‐(SH3 domain)–binding protein 1 (G3BP1) primes cGAS for its prompt activation by engaging cGAS in a primary liquid‐phase condensation state. Using high‐resolution microscopy, we show that in resting cells, cGAS exhibits particle‐like morphological characteristics, which are markedly weakened when G3BP1 is deleted. Upon DNA challenge, the pre‐condensed cGAS undergoes liquid–liquid phase separation (LLPS) more efficiently. Importantly, G3BP1 deficiency or its inhibition dramatically diminishes DNA‐induced LLPS and the subsequent activation of cGAS. Interestingly, RNA, previously reported to form condensates with cGAS, does not activate cGAS. Accordingly, we find that DNA – but not RNA – treatment leads to the dissociation of G3BP1 from cGAS. Taken together, our study shows that the primary condensation state of cGAS is critical for its rapid response to DNA. Synopsis Host cell encoded cGAS is a critical DNA sensor to detect invading pathogens. The stress‐granule protein G3BP1 engages cGAS in a primary condensation state to enable a rapid response to free DNA. G3BP1 primes cGAS for its prompt activation. G3BP1 engages cGAS in a primary condensation state. DNA‐ but not RNA‐interaction leads to the dissociation of G3BP1 from cGAS. Green tea compound epigallocatechin gallate (EGCG) inhibits G3BP1‐promoted cGAS phase condensation and activation. Graphical Abstract Host cell encoded cGAS is a critical DNA sensor to detect invading pathogens. The stress‐granule protein G3BP1 engages cGAS in a primary condensation state to enable a rapid response to free DNA.