[Preparation of liposomes entrapping plasmid DNA and linear DNA]

Liposomes entrapping plasmids pSV2-neo DNA, pUC18-ras DNA, pSV2-neo-ras DNA and linear DNA were prepared. The liposomes were composed of DOPC/Chol/OA (4:4:3) and pH-sensitive DOPE/Chol/OA (4:4:3), respectively. The efficiency of DNA entrapment was about 50%. Gel electrophoresis analysis showed: Liposome-entrapped DNA was not digested by DNase; The entrapped DNA molecules were intact and stable for at least 5-6 months at 4 degrees C. During preparation of pH-sensitive liposome, the pH must be kept at 8.0.