DNA-Induced Aggregation and Fusion of Phosphatidylcholine Liposomes in the Presence of Multivalent Cations Observed by the Cryo-TEM Technique

By means of cryoelectron transmission microscopy (cryo-TEM), we were able to demonstrate the formation of ternary complexes (TC): DNA–phosphatidylcholine liposome–divalent metal cations. Addition of Ba²⁺ to TC led to visualization of DNA compacting on the liposome surface. Staining the TC by Tb³⁺ cations revealed the changed secondary structure of DNA located between fused liposomes. Cryo-TEM and liposome turbidity data were analyzed during TC formation. Liposome aggregation and the liposome fusion induced by DNA in TC were observed. Because TC displayed the property of DNA cationic liposome complexes as well as their own unique properties, we were able to consider cationic lipoplexes as a particular case of TC. The involvement of TC and direct DNA–lipid interactions in the formation nuclear pore complexes were assumed.