Cells were cultured under standard conditions of 10% FBS in DMEM. G3BP1-knockout (KO) mouse embryonic fibroblasts (MEFs) were a kind gift from Sophy Martin and Jamal Tazi (CNRS, France) (46 (link)). For analysis of G3BP1-induced stress granules, G3BP1 expression constructs were transfected using Fugene HD under conditions optimized for SG induction, as previously described (Promega) (6 (link)). For expression of other transgenes, cells were transfected with Fugene HD in 2% FBS-DMEM overnight and harvested the following day for analysis. This procedure typically yielded greater than 70% transfection efficiency for GFP expression constructs. siRNAs were performed with a neon electroporation device (Life Technologies) in accordance with the manufacturer’s instructions. siRNAs were transfected at 500 pmol per 3 million cells. siRNA experiments were harvested 48 or 72 h posttransfection. Arsenite was used at 500 µM for 30 min at 37°C for experiments in which arsenite was used as a control for eIF2α phosphorylation.