Different proportions of cholesterol and CS in GUVs modulate domain size, domain curvatures, budding, and the formation of tubular structures. GUVs consisted of 42% DOPC, 42% SM, and 16% of sterol mixture (cholesterol and CS). Proportions of cholesterol and CS are indicated. Labeling is the same as in . A transition from clear phase separation (A; 16% cholesterol) to no observable domains (C; 0% cholesterol) occurs. At 8% cholesterol and 8% CS, a majority of GUVs show small domains that do not fuse to yield larger ones (B). At more CS, GUVs look mostly uniform (C). Confocal sections in D–G represent curvatures of GUVs at the cholesterol and CS concentrations indicated. At 16% cholesterol, curvature is predominantly positive. With an increasing fraction of CS, bell-shaped lo domains with a negative curvature close to the borders with the ld domains are observed (E and F). As seen in the time series (F), at the edges, small lo phase vesicles bud inward (arrow). At higher CS concentrations (G), no domains but many tubular and reticular structures, are observed. (Scale bar: 10 μm.)