查看文章

We discovered that several high molecular weight cationic polymers, such as poly(l-lysine) and protamine, can enhance the transfection efficiency of several types of cationic liposomes by 2-28-fold in a number of cell lines in vitro. Small polycations such as spermine and a cationic decapeptide derived from SV40 T-antigen were only moderately active. The addition of poly(l-lysine) and protamine dramatically reduced the particle size of the complex formed between DNA and cationic liposomes and rendered DNA resistant to the nuclease activity. The complexes composed of DNA, poly(l-lysine), and cationic lipids were purified from an excess of free liposomes with sucrose gradient ultracentrifugation. Purified complex formed at low cationic liposome ratio was poor in lipid content and only had weak transfection activity. Addition of free liposome to the purified complex significantly enhanced the transfection activity. In …