Figure 2.

G4-RNA promotes the formation of FUS condensates.A and B, CD spectrum of model G4-RNAs. Two species of G4-RNA (PSD-94 and CaMKIIα) were subjected to CD spectroscopic analysis in the presence (NaCl) and absence (Control) of Na⁺. The CD spectrum has a positive peak near 265 nm and a negative peak near 245 nm, both of which are characteristic of the parallel stranded G4-RNA structure. PSD-95 G4 contains four-A-loop between the first and second G triplet. C, influence of G4-RNAs on the formation of FUS condensates. Purified FUS protein (2 μM) was mixed with each of G4-RNAs or a reference randomized RNA (n20), and the level of FUS condensate formation was determined by measuring the turbidity. The graph shows the turbidity value of FUS solution in the presence of increasing RNA concentrations. The turbidity (y-axis) represents the average of three independent experiments together with ±SEM values. In the absence of protein, no condensate was observed. Statistical significance was determined by two-tailed Student's t test ∗∗p < 0.01, ∗∗∗p < 0.001. Representative images of the phase-contrast microscopy are shown for each. Scale bar represents 20 μm. D, FUS condensates were formed in the presence of terminal fluorescent-labeled G4 RNAs (2 μM). FUS condensates formed were observed with fluorescent microscopy. Using the same concentration of BSA (2 μM), no fluorescent signal was detected.