association of mRNAs with stress granules may simply be a side effect of the association of partially unfolded RNA-binding proteins with stress granules, similar to the association of mRNAs with proteasomes. Formation Environmental stressors trigger cellular signaling, eventually leading to the formation of stress granules. In vitro, these stressors can include heat, cold, oxidative stress (sodium arsenite), endoplasmic reticulum stress (thapsigargin), proteasome inhibition (MG132), hyperosmotic stress, ultraviolet radiation, inhibition of eIF4A (pateamine A, hippuristanol, or RocA), nitric oxide accumulation after treatment with 3-morpholinosydnonimine (SIN-1), perturbation of pre-mRNA splicing, and other stressors, like puromycin, which result in disassembled polysomes. Many of these stressors result in the activation of particular stress-associated kinases (HRI, PERK, PKR, and GCN2), translational inhibition and stress granule formation. Stress granule formation is often downstream of the stress-activated phosphorylation of eukaryotic translation initiation factor eIF2α; this does not hold true for all types of stressors that induce stress granules, for instance, eIF4A inhibition. Further downstream, prion-like aggregation of the protein TIA-1 promotes the formation of stress granules. The term prion-like is used because aggregation of TIA-1 is concentration dependent, inhibited by chaperones, and because the aggregates are resistant to proteases. It has also been proposed that microtubules play a role in the formation of stress granules, perhaps by transporting granule components. This hypothesis is based on the fact that disruption of microtubules with the chemical nocodazole blocks the appearance of the granules. Furthermore, many signaling molecules have been shown to regulate the formation or dynamics of stress granules; these include the "master energy sensor" AMP-activated protein kinase (AMPK), the O-GlcNAc transferase enzyme (OGT), and the pro-apoptotic kinase ROCK1. Potential roles of RNA-RNA interactions RNA phase transitions driven in part by intermolecular RNA-RNA interactions may play a role in stress granule formation. Similar to intrinsically disordered proteins, total RNA extracts are capable of undergoing phase separation in physiological conditions in vitro. RNA-seq analyses demonstrate that these assemblies share a largely overlapping transcriptome with stress granules, with RNA enrichment in both being predominately based on the length of the RNA. Further, stress granules contain many RNA helicases, including the DEAD/H-box helicases Ded1p/DDX3, eIF4A1, and RHAU. In yeast, catalytic ded1 mutant alleles give rise to constitutive stress granules ATPase-deficient DDX3X (the mammalian homolog of Ded1) mutant alleles are found in pediatric medulloblastoma, and these coincide with constitutive granular assemblies in patient cells. These mutant DDX3 proteins promote stress granule assembly in