Figure 1.

Cations mediate bridging between DNA and gel-phase PC bilayers. (a) Representative confocal micrographs and schematic depiction of the interaction between DPPC GUVs and Cy3-labeled dsDNA in buffers with and without magnesium salt added, as observed at room temperature and upon heating above the phase transition temperature (T_m) of lipids. Scale bars: 5 μm. (b) Representative confocal micrographs of DPPC GUVs showing gradual detachment of the dsDNA with the temperature increasing above T_m. Scale bar: 5 μm. (c) Temperature dependence of the attachment of DNA constructs to DPPC GUVs recorded via fluorescence upon heating (red points). The turquoise data points were collected on cooling the sample down, illustrating reversibility of the process. The error bars indicate the standard deviation from three independent experiments. (d) Differential scanning calorimetry (DSC) plot of DPPC large unilamellar vesicles (LUVs) incubated with dsDNA in the presence of Mg²⁺. The position of the peak indicates the transition temperature (T_m) of the membrane. An analogous curve was obtained for lipid samples lacking DNA or cations (Figure S4). (e) Dependence of the DNA attachment on bilayer phase, as modulated by changing cholesterol molar fraction in DPPC/cholesterol binary mixtures. For GUVs displaying gel–L_o phase coexistence (cholesterol/DPPC molar ratio of 15%) the DNA is localized in parts which presumably correspond to the gel-phase domains (Figure S10). Scale bars: 10 μm. (f) Representative confocal micrograph demonstrating the lack of DNA attachment on liquid disordered POPC/cholesterol GUV. Scale bar: 10 μm.