Single-molecule visualization of interaction between DNA and oppositely charged mixed liposomes

The interaction between large single phage T4 DNA and mixed cationic diocta decyldimethylammonium bromide/dioleoyl phosphatidylethanolamine (DODAB/DOPE ) liposomes was studied with the use of a fluorescence microscopy technique . It was found that interaction started at very low liposome concentrations , far below the concentration of DNA. Also, the DNA size distribution was b imodal in a wide range of liposome concentrations. The critical concentrati on of the cationic lipid needed for the complete collapse of single DNA mol ecules strongly depended on the composition of the charged mixed DODAB/DOPE liposomes. The effect is supposed to be due to the concurrence between DNA -DODAB complex formation and DODAB incorporation into mixed liposomes with DOPE. In addition, the liposome surface charge density, which is dependent on the liposome composition and increases with the increase of the molar fr action of DOPE in the mixed liposome, is assumed to be a possible important factor. The report emphasizes the importance of the use of single-molecule detection methods in the DNA-liposome interaction studies.