The study investigates the role of the prion-like domain (PRD) of TIA-1, an RNA-binding protein, in the assembly of stress granules (SGs). TIA-1 promotes the formation of SGs, which are cytoplasmic inclusions that contain stalled translation initiation complexes in response to environmental stress. The PRD of TIA-1 exhibits characteristics of prions, including concentration-dependent aggregation, resistance to protease digestion, and induction of heat shock protein (HSP)70. Overexpression of the PRD forms cytoplasmic microaggregates that sequester endogenous TIA-1 and TIAR, preventing SG assembly. The prion-like domain of the yeast prion SUP35 can substitute for the TIA-1 PRD in promoting SG assembly. The aggregation of the PRD is regulated by HSP70, which is induced by the aggregated PRD. TIA-1 knockout mouse embryonic fibroblasts (MEFs) exhibit impaired ability to form SGs, suggesting that TIA-1 is crucial for SG assembly. The findings indicate that prion-like aggregation of TIA-1 regulates SG formation downstream of eIF2α phosphorylation in response to stress.The study investigates the role of the prion-like domain (PRD) of TIA-1, an RNA-binding protein, in the assembly of stress granules (SGs). TIA-1 promotes the formation of SGs, which are cytoplasmic inclusions that contain stalled translation initiation complexes in response to environmental stress. The PRD of TIA-1 exhibits characteristics of prions, including concentration-dependent aggregation, resistance to protease digestion, and induction of heat shock protein (HSP)70. Overexpression of the PRD forms cytoplasmic microaggregates that sequester endogenous TIA-1 and TIAR, preventing SG assembly. The prion-like domain of the yeast prion SUP35 can substitute for the TIA-1 PRD in promoting SG assembly. The aggregation of the PRD is regulated by HSP70, which is induced by the aggregated PRD. TIA-1 knockout mouse embryonic fibroblasts (MEFs) exhibit impaired ability to form SGs, suggesting that TIA-1 is crucial for SG assembly. The findings indicate that prion-like aggregation of TIA-1 regulates SG formation downstream of eIF2α phosphorylation in response to stress.