The study investigates the role of G3BP, a phosphorylation-dependent endoribonuclease that interacts with RasGAP, in the assembly of stress granules (SGs). G3BP is recruited to SGs in cells exposed to arsenite, suggesting its involvement in determining mRNA fate during cellular stress. The assembly of SGs can be induced by overexpression of G3BP or inhibited by expressing a central domain of G3BP, which binds RasGAP and contains serine 149, whose dephosphorylation is induced by arsenite treatment. A phosphomimetic mutant (S149E) fails to oligomerize and assemble SGs, while a nonphosphorylatable mutant (S149A) does both. These findings indicate that G3BP is an effector of SG assembly, and that Ras signaling contributes to this process by regulating G3BP dephosphorylation. The study also explores the modular organization of G3BP and the role of its different domains in SG recruitment and assembly.The study investigates the role of G3BP, a phosphorylation-dependent endoribonuclease that interacts with RasGAP, in the assembly of stress granules (SGs). G3BP is recruited to SGs in cells exposed to arsenite, suggesting its involvement in determining mRNA fate during cellular stress. The assembly of SGs can be induced by overexpression of G3BP or inhibited by expressing a central domain of G3BP, which binds RasGAP and contains serine 149, whose dephosphorylation is induced by arsenite treatment. A phosphomimetic mutant (S149E) fails to oligomerize and assemble SGs, while a nonphosphorylatable mutant (S149A) does both. These findings indicate that G3BP is an effector of SG assembly, and that Ras signaling contributes to this process by regulating G3BP dephosphorylation. The study also explores the modular organization of G3BP and the role of its different domains in SG recruitment and assembly.