Electric impulses (8 kV/cm, 5 microseconds) were found to increase greatly the uptake of DNA into cells. When linear or circular plasmid DNA containing the herpes simplex thymidine kinase (TK) gene is added to a suspension of mouse L cells deficient in the TK gene and the cells are then exposed to electric fields, stable transformants are formed that survive in the HAT selection medium. At 20 degrees C after the application of three successive electric impulses followed by 10 min to allow DNA entry there result 95 (+/‐ 3) transformants per 10(6) cells and per 1.2 micrograms DNA. Compared with biochemical techniques, the electric field method of gene transfer is very simple, easily applicable, and very efficient. Because the mechanism of DNA transport through cell membranes is not known, a simple physical model for the enhanced DNA penetration into cells in high electric fields is proposed. According to this ‘electroporation model’ the interaction of the external electric field with the lipid dipoles of a pore configuration induces and stabilizes the permeation sites and thus enhances cross membrane transport.

No abstract

Stable transformation of mouse L cells deficient in thymidine kinase was achieved by liposome-mediated transfer of a recombinant plasmid carrying the thymidine kinase gene. Ten percent of the recipient cells expressed thymidine kinase activity. The transformed phenotype (for example, 200 out of 10(6) cells) was stable under selective and nonselective conditions. The liposome technique is compared with other methods currently used for gene transfer.

Three diastereomeric pairs of diol epoxides, two tetrahydro-epoxides, and the K-region oxide of the polycyclic aromatic hydrocarbon benz[alanthracene were evaluated for mutagenic activity in strain TA 100 of Salmonella typhimurium and in line V79-6 of Chinese hamster lung cells. The two diastereomeric 1,2-epoxides of the trans-3,4-dihydrodiol of benz[alanthracene are 15 to 35 times more mutagenic to the bacteria and 65 to 125 times more mutagenic to the mammalian cells than are the diastereomeric pairs of benz[ajanthracene-8,9-diol-10,11-epoxides or benz[alanthracene-10,11-diol-8,9-epoxides. 1,2-Epoxy-1,2,3,4-tetrahydrobenzlajanthracene is the most mutagenic and cytotoxic of the nine derivatives and is 5 and 25 times more mutagenic than 3,4-epoxy-1,2,3,4-te-