with known protein markers of stress granules (immunocytochemistry). In 2016, stress granule "cores" were experimentally identified and then biochemically purified for the first time. Proteins in the cores were identified in an unbiased manner using mass spectrometry. This technical advance lead to the identification of hundreds of new stress granule-localized proteins. The proteome of stress granules has also been experimentally determined by using two slightly different proximity labeling approaches. One of these proximity labeling approaches is the ascorbate peroxidase (APEX) method, in which cells are engineered to express a known stress granule protein, such as G3BP1, fused to a modified ascorbate peroxidase enzyme called APEX. Upon incubating the cells in biotin and treating the cells with hydrogen peroxide, the APEX enzyme will be briefly activated to biotinylate all proteins in close proximity to the protein of interest, in this case G3BP1 within stress granules. Proteins that are biotinylated can then be isolated via streptavidin and identified using mass spectrometry. The APEX technique was used to identify ~260 stress granule-associated proteins in several cell types, including neurons, and with various stressors. Of the 260 proteins identified in this study, ~143 had not previously been demonstrated to be stress granule-associated. Another proximity labeling method used to determine the proteome of stress granules is BioID. BioID is similar to the APEX approach, in that a biotinylating protein (BirA* instead of APEX) was expressed in cells as a fusion protein with several known stress granule-associated proteins. Proteins in close proximity to BirA* will be biotinylated and are then identified by mass spectrometry. Youn et al. used this method to identify/predict 138 proteins as stress granule-associated and 42 as processing body-associated. A curated database of stress granule-associated proteins can be found here . The following is a list of proteins that have been demonstrated to localize to stress granules (compiled from ): References Further reading — molecular details of stress granule assembly & function External links Laboratories: Anderson lab, post-transcriptional control & inflammatory response Zhou lab, neurodegenerative disease Morimoto lab, transcriptional regulation & heat shock Boccaccio lab, Staufen & stress granules Cell biology