||P.836 left column bottom paragraph: "The number of SVs present was measured by fluorescence correlation spectroscopy (FCS), which is a reliable standard way of counting particles in solution (Magde et al., 1972, Muller et al., 2003). Vesicles were labeled with the membrane dye FM1-43, which only becomes fluorescent upon membrane insertion. Addition of vesicles to buffer containing FM1-43 increased the emitted light intensity severalfold (Figure 2A)."
||P.836 right column top paragraph: "A strong time-dependent autocorrelation (Figure 2B, bottom, black lines) for fluctuations in the signal (Figure 2B, top) was observable, which was only seen when vesicles were added (Figure 2B, bottom, red line). For each sample, the protein concentration was determined in parallel. Based on the FCS counts, the following average values were then calculated for single vesicles: protein = (17.1 ± 0.19) × 10^−18 g/vesicle (Figure 2C), phospholipids = 8.8 × 10^−18 g/vesicle, and cholesterol = 3.7 × 10^−18 g/vesicle, resulting in a total predicted dry mass of 29.6 × 10^−18 g/vesicle (Table 2, see also Supplemental Data)."