We have investigated the use of liposomes as carriers for the transfer of simian virus 40 (SV40) DNA into mammalian cells. The amount of DNA entrapped in liposomes was dependent on the input DNA concentration and lipid composition. DNA remained intact after liposome encapsulation and was resistant to deoxyribonuclease digestion. Combined transfer to and expression of liposome-entrapped SV40 DNA in monkey kidney cells was assayed by infectious plaque formation. Negatively-charged liposomes containing phosphatidylserine were more effective in DNA transfer and expression than neutral liposomes. The inclusion of carrier salmon sperm DNA inhibited liposome-entrapped SV40 DNA infectivity. Infectivity of liposome-entrapped DNA was directly related to both liposome DNA concentration and number of vesicles added. Liposome-entrapped SV40 minichromosome was 20-fold more infective than free minichromosome, but only 20% more infective than liposome-entrapped SV40 DNA. Thus, the presence of hyperacetylated histones on the DNA failed to enhance liposome-mediated DNA transfer appreciably. Incubation of cells with various modulators of endocytosis implicated the endocytotic pathway in the mechanism of liposome-mediated DNA transfer. These studies show that liposomes are suitable carriers for the introduction of viral DNA and chromatin into mammalian cells.
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