Figure 2.

Quantification of nonequilibrium coacervate shapes by average circularity of cross sections. (a) Schematic depiction of PNPase reaction in the presence of poly(U)/spermine coacervates in equilibrium, supplemented with poly(U) seeds, UDP, and PNPase. Initially, the coacervates become active but as the reaction reaches a dynamic equilibrium (t → ∞), they assume their spherical equilibrium shape. (b,c) PNPase reaction in the presence of preformed coacervates with 1 μM (b) and 4 μM (c) PNPase. There is a significant qualitative difference in terms of the coacervate shapes prior to assuming a spherical equilibrium shape. Images are false-colored and the scale bar indicates 10 μm. (d) Plot of the average circularity of coacervate cross sections for PNPase concentrations of 4 μM (black), 2 μM (red), and 1 μM (blue) PNPase. The control (green) contained passive poly(U)_∞/spermine coacervates, which were produced by incubation of PNPase, poly(U)₂₀, and UDP (see Materials and Methods for details). Dashed lines indicate the minimum observed average circularity per condition. In all images, PNPase was added 5 min before the start of image acquisition. (e) Average circularity profiles for 20 mM (black), 5 mM (red), and 2 mM (blue) UDP. (f) Average circularity profiles for temperatures of 30 °C (black), 34 °C (red), and 26 °C (blue). In panels d–f, the error bars indicate standard error from the mean.