Preferential G3BP1-induced condensation of DNA-RNA mixtures from stress granules over RNA or double-stranded DNA.

G3BP1 is a regulator of stress granule assembly capable of driving condensation of RNA in vitro. Recently, we purified stress granule cores from yeast and mammalian cells, and found that in addition to RNA and proteins, they contain large amounts of circular double-stranded DNA (dsDNA). Since G3BP1 has been implicated in DNA-RNA heteroduplex resolution, we compared the ability of G3BP1 to drive condensation of cytoplasmic RNA, circular cytoplasmic dsDNA, and total nucleic acids (comprising both, circular dsDNA and RNA) extracted from purified stress granule cores of HEK293T cells. Imaging under near-physiologic conditions (1.7 mM MgCl2, no crowding agents, 0.1 ng/μL nucleic acids) revealed that G3BP1 most effectively induces condensation of the DNA-RNA mixture from stress granule cores. Comparison of the disruption of these condensates by treatment with RNase A, DNase, or RNase H further shows that they are especially susceptible to the latter two. The sensitivity to DNase and RNase H of G3BP1-induced condensates of the stress granule-derived nucleic acid mixtures underscores the importance of DNA in these cytoplasmic assemblies.