The introduction of foreign DNA sequences into mammalian cells mediated by DNA transfection is a basic method in modern molecular biology. Several different DNA transfection methods are currently used that have varying efficiencies dependent on the type of cell and its growth status. However, none of the available approaches has been shown to lead to transfection of growth arrested cells in culture at an appreciable level. In this report we show that poly-L-ornithine combined with a DMSO shock mediates efficient transfection of both growing and resting cells.

Polybrene (1), a poly cation, allows transfection of Chinese hamster ovary (CHO) cells with either plasmid or genomic DNA at an efficiency about 10-fold greater than calcium phosphate mediated gene transfer (2). Because of the relatively high transfection rate observed with polybrene, we examined the relative efficiencies of various other polycations for their ability to transfect CHO cells. In stable transfections using pSV2neo and G418 selection (2) and a similar protocol to that described for polybrene (2), poly-L-ornithine produced the highest rate of transfection (7.0±2.2 xlO4 colonies//ig DNA/5 XlO5 cells), significantly higher than poly-L-lysine (1.3±0.6 X104 colonies//tg DNA/5 X105 cells) which gave comparable results to polybrene (1.2±0.6 X104 colonies//tg DNA/5 XlO5 cells). In transient transfections with pCHO (Pharmacia), a/3-