Figure 2. RNA-spermine mixtures have coexisting LCST and UCST phase transitions.

(a) Bright-field images of poly(rU)-spermine mixtures at different temperatures showing an LCST and a subsequent UCST transition. The sample was prepared by mixing poly(rU) and spermine (Sp⁺⁴) at final concentrations of 1.5 mg/ml and 60 mM, respectively, in a buffer containing 25 mM Tris-HCl (pH 7.5). Scale bar represents 10 µm. (b) Temperature phase diagram of poly(rU)-spermine mixtures at different spermine concentrations. Solid symbols indicate temperatures of droplet formation (T_phase) and open symbols indicate temperatures of droplet dissolution (T_clear). Here, poly(rU) concentration was kept fixed at 1.5 mg/ml in 25 mM Tris-HCl buffer (pH 7.5). Shaded regions indicate the conditions where phase separation occurs. Solid line is drawn as a guide to the eye.