Using a plasmid containing the bacterial chloramphenicol acetyl transferase gene, we have assayed for transient expression of DNA introduced into mouse L cells by a variety of transfection conditions. High efficiency uptake and expression of this foreign DNA have been achieved by modifying the DEAE dextran mediated trsnafection procedure of McCutchan and Pagano (1) to include a shock with either dimethyl sulfoxide or glycerol. Inclusion of the shock step can increase expreasion of the transfected gene a surprising ̃50 fold. With plasmid constructs that do not replicate after transfection, we can readily detect CAT activity in an overnight autoradiographic exposure from less than 0.1% of an extract from a 60 mm dish of transfected cells. We have determined the amounts of DNA, the amount and time course of DEAE-dextran and dimethyl aulfoxide treatments, the effects of additional DNA, and the time after transfection which yield maximal expression. Overall, this transfection protocol using DEAE-dextrsn coupled to a shock treatment is simple, straightforward, and gives consistently high levels of expression of the input DNA.
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