HeLa cells. In mammalian cells, RHAU mutants lead to reduced stress granule dynamics. Thus, some hypothesize that RNA aggregation facilitated by intermolecular RNA-RNA interactions plays a role in stress granule formation, and that this role may be regulated by RNA helicases. There is also evidence that RNA within stress granules is more compacted, compared to RNA in the cytoplasm, and that the RNA is preferentially post-translationally modified by N6-methyladenosine (m6A) on its 5' ends. Recent work has shown that the highly abundant translation initiation factor and DEAD-box protein eIF4A limits stress granule formation. It does so through its ability to bind ATP and RNA, acting analogously to protein chaperones like Hsp70. Connection with processing bodies Stress granules and P-bodies (processing bodies) share RNA and protein components, both appear under stress, and can physically associate with one another. As of 2018, of the ~660 proteins identified as localizing to stress granules, ~11% also have been identified as processing body-localized proteins (see below). The protein G3BP1 is necessary for the proper docking of processing bodies and stress granules to each other, which may be important for the preservation of polyadenylated mRNAs. Although some protein components are shared between stress granules and processing bodies, the majority of proteins in either structure are uniquely localized to either structure. While both stress granules and P-bodies are associated with mRNAs, processing bodies have been long proposed to be sites of mRNA degradation because they contain enzymes like DCP1/2 and XRN1 that are known to degrade mRNAs. However, others have demonstrated that mRNAs associated with processing bodies are largely translationally repressed but not degraded. It has also been proposed that mRNAs selected for degradation are passed from stress granules to processing bodies, though there is also data suggesting that processing bodies precede and promote stress granule formation. Protein composition of stress granules The complete proteome of stress granules is still unknown, but efforts have been made to catalog all of the proteins that have been experimentally demonstrated to transit into stress granules. Importantly, different stressors can result in stress granules with different protein components. Many stress granule-associated proteins have been identified by transiently stressing cultured cells and utilizing microscopy to detect the localization of a protein of interest either by expressing that protein fused to a fluorescent protein (i.e. green fluorescent protein (GFP)) and/or by fixing cells and using antibodies to detect the protein of interest along