Fig. 1.

SH3₅–PRM₅ mixtures readily phase separate at room temperature and physiological salt concentration. (A) Representative structures of SH3₅ (magenta, SH3 domains; cyan, inter-SH3 linkers) and PRM₅ (blue, proline-rich motifs; yellow, inter-PRM linkers). (B) Phase diagram of SH3₅–PRM₅ mixtures in 10 mM imidazole buffer, pH 7, with 150 mM KCl. The red dots indicate phase separation, and the blue crosses indicate no phase separation. The black curve bordering the pink-shaded region is obtained by fitting the midpoints between phase-separated and non–phase-separated regions to the following set of parametric equations:

$$x=\left(a{\left[1+{\left(\left|t\right|/b\right)}^c\right]}^{1/c}-t\right)/\sqrt{2},$$

$$y=\left(a{\left[1+{\left(\left|t\right|/b\right)}^c\right]}^{1/c}+t\right)/\sqrt{2},$$

with a = 19.3 µM, b = 12.1 µM, and c = 4. For the portion of the boundary curve shown, t runs from −27 to 27 µM. (C) Confocal bright-field images of SH3₅–PRM₅ droplets at different equimolar concentrations of the 2 components.